I'll try to put in some filler here. This is information copied from Spoilerfix.com. Information on first several episodes and some potential spoilers which the site disclaims by saying may or may not be accurate.

Enough filler?

Special: Lost - A Tale of Survival
Airdate: September 27, 2006

09/11 - Feeling lost? Having a hard time keeping up with what’s happening on the island? ABC has the remedy for what ails you by inviting both new and avid “Lost” viewers to take an insider’s look at the most talked about, critically acclaimed show on television. “Lost: A Tale of Survival” will explore the series in a way that will bring new viewers up to date, but which current viewers will also find illuminating. From the back stories of some of the most compelling characters on television to the mysteries of the island, “Lost: A Tale of Survival” will provide an insightful glimpse into the lives of the survivors of Oceanic Airlines flight 815. Source: ABC

Episode 3.01: A Tale of Two Cities (Jack-centric)
Airdate: October 4, 2006

09/18 - Guest starring are John Terry as Christian Shephard, Julie Bowen as Sarah, M.C. Gainey as Mr. Friendly, William Mapother as Ethan, Brett Cullen as Goodwin, Blake Bashoff as Karl, Julie Adams as Amelia, Stephen Semel as Adam, Isabelle Cherwin as little girl, Alexandra Morgan as moderator, Sonya Seng as receptionist, Sally Davis as teacher and Julie Ow as nurse. Source: ABC
09/14 - In the season premiere episode, "A Tale of Two Cities," Jack, Kate and Sawyer begin to discover what they are up against as prisoners of "The Others." John Terry and Julie Bowen guest star. Source: ABC
09/14 - The opening scene of the Oct. 4 premiere will be very reminiscent of the first scene from last season's premiere, with Desmond in the hatch. In other words, you're probably going to be asking yourself, "Who's that and where the hell are we?!" Source: Ask Ausiello @ TV Guide
09/11 - We'll see more of why he feels so guilty about his dad. Jack is in a glass enclosure, and will be interacting a lot with a character we haven't yet seen. Kate is in an examining room, and will be interacting with a character we know! Source: Kristin on E!Online
08/29 - Expanding on the 08/19 spoilers posted below on the Jack's flashback with the choking girl in the park: Also in that scene, Sarah is talking to a male teacher who may be more than a friend, and a little girl (the choking girl?) ends the scene by telling Jack not to trust Sarah. Source: The Transmission
08/24 - Matthew Fox was on set shooting flashback scenes with Julie Bowen (who plays Jack's wife, Sarah). Source: USA Today
08/19 - According to pictures that leaked on the net, there will be a flashback where Jack performs the Heimlich manoeuvre on a little blond girl in a park. Source: Dryope
08/18 - Jack was just shooting a flashback all decked out in his hospital scrubs. Kate will be making a choice in the first six episodes. Jack is inside something you’d find in a science class. Kate is on something we’ve seen before. And Sawyer is surrounded by something through which he shares a connection with Jack’s father. Source: Kristin on E!Online
07/29 - This episode will be Kate-centric and have flashbacks featuring a 60-year-old motherly, warm, and funny woman as well as handsome twenty-year-old Karl. Source: SpoilerFix.com
07/21 - During an interview Carlton Cuse revealed: We pick up where we left off, but obviously there are different stories on different parts of the island, and, you know, we will get to all of them in the first few episodes. But like last year, we didn't deal with the raft survivors in the first episode. Not everything is going to be answered in the first episode. But the captivity story will definitely be addressed.Source: The Ausiello Report

Episode 3.02: Further Instructions (Locke-centric)
Airdate: October 11, 2006

09/20 - The Oct. 11 episode, called "Further Instructions," will also reveal what happened to Locke, Desmond and Eko when the hatch collapsed in last season's finale, and will find Hurley returning to camp after being released by the Others. "Ian Somerhalder guest stars as Boone," the network copy says. Source: Zap2it
09/14 - Ian Somerhalder who played Boone, the first major characters to buy-it in season one, on the hit series LOST has come back for another go around. Only this time, it's not popping up inexplicably in someone's flashback, as you might guess. Hot off the release of his big screen horror "Pulse", the former LOST star spent a week in Hawaii working on new material for an upcoming episode of LOST which centers on the bushman-who-lost-his-way John Locke. In the episode Locke, who is still reeling from his actions in the cataclysmic season finale, begins to have visions of the young man who died to keep the hatch a secret. Boone leads Locke to a redemption of sorts and sets him off on a "kung fu" like journey to unravel yet another island mystery. Sources say this journey rivals the season one fascination with the hatch and will find John Locke squarely returning to his mysterious mysticism and McGyver-ish ways. Source: BuddyTV
08/29 - A scene was filming at the Hawaii Convention Center today, a Locke flashback (?) at the Sydney International Airport. I saw Locke in his chair, but he was shirtless. He seemed to be pointing or gesturing as he's pushed through the crowd of travelers. It almost seemed like it was a "dream sequence." Source: The Transmission
08/17 - The flashbacks also features Eddie, a sweet but torn caucasian male in his 20s. There will also be a trooper in his 30s. Source: SpoilerFix.com
08/09 - It's Claire-centric and her flashback features Mike and Jan, a hippie-ish couple in their 50's. They are warm and kind, but also tough and protective when the situation calls for it. Source: secretagentman @ TWOP

Episode 3.03: The Glass Ballerina (Sun/Jin-centric)
Airdate: October 18, 2006

08/30 - Colleen is set to have been a security officer when she was off the island. Source: SpoilerFix.com
08/29 - New character introduced in #303. Will recur. 'Colleen', late 30's, tough, obvious military training. Doesn't flinch when a gun is shoved in her face. Trusts few people on the island and only allows herself to be emotionally vulnerable in front of her significant other. Source: secretagentman @ TWOP
08/18 - Sun has a dream of her future, featuring her 9-year-old daughter. Source: secretagentman @ TWOP

Episode 3.04: Every Man For Himself (Desmond-centric)
Airdate: October 25, 2006

09/07 - Amongst Desmond's flashbacks, we will see his best friend in prison, Stuckey Chavez. The latter is not the sharpest knife in the drawer but he is always appraised of prison gossip. Source: SpoilerFix.com
08/22 - Desmond-centric flashbacks of his time in prison. It features Warden Harris, a nasty man with a hate for Desmond. 'Munson', a mild-mannered gov't bureaucrat in his 30's who shows his dark side when he finds out he has been betrayed by his wife. Source: secretagentman @ TWOP

Episode 3.05: The Cost of Living (Eko-centric)
Airdate: November 1, 2006

09/06 - This Eko-centric episode will feature a Nigerian woman named Amadi who is intuitive and strong and has a son, a violent warlord named Azi, and a sweet altar boy named Daniel. Source: SpoilerFix.com

General spoilers:

09/19 - I've only seen two beings : (a) a character we knew from before and (b) the cutest little fuzziest more adorable animal (that is not Vincent the dog). Source: Kristin on E!Online
09/15 - You wanna know where the Others live? I'll tell you. In the last place you'd expect. And that's just one of the jaw-dropping twists you'll discover in the first few episodes of the third season of Lost. Those frustrated with the lack of answers last season will be happy to get a few in the first few episodes--like, oh, the revelation of what the Others are up to, what shocking connection Jin has to Sun's secret lovah and which island boy will be once again kissing Kate. Yep, kissing her. A few old faces will even be coming back, like William Mapother (Ethan), Ian Somerhalder (Boone) and, hopefully, more of Cynthia Watros (Libby) in flashbacks. Source: Kristin on E!Online
09/11 - I can tell you that at some point in the first four episodes, does confess that she loves someone on the island. It is one of the most heart-wrenching (in every single possible meaning of the phrase “heart-wrenching”) scenes you will ever see. Despite what Rodrigo Santoro said in that interview with a Brazilian newspaper, actually appears very early on this season, and he will be one-half of the one of the hottest couples I think I’ve ever seen on television. is not a plane crash survivor. She is a woman. She is romantically linked to someone we already know, and could be romantically linked to a second someone we know. Source: Kristin on E!Online
08/29 - Damon Lindelof revealed: Elizabeth Mitchell is a regular, while Rodrigo and Kiele are contracted to be recurring characters. When we meet up with the three castaways (held captive by the Others), Sawyer is in a cage! The planned series finale of Lost a "happy but tragic" ending. Source: Kristin on E!Online
08/25 - A little birdie told me William Mapother was in Hawaii last week -- and he exactly wasn't sipping mai tais by the pool, but rather, he was working his wonderfully creepy Ethan magic. Simply put in the words of executive producer Bryan Burke: "The Hatch is gone. Done. We have new sets that have been built on our soundstage, so it's a whole new world for you." It looks as if Kate is spending some quality time in close quarters with good ol' Henry. Rodrigo said that he won't appear on the show until February. Turns out, Rodrigo is still under contract with Globo TV. He said they're letting him take a sabbatical to shoot Lost, and then he'll go back to Globo, so it doesn't sound like he'll be sticking around all that long in Hawaii. Rodrigo said, "I'm going to be one of the survivors from the plane that apparently was on the island all this time. I'm going to be a character with a past." Terry O'Quinn revealed that "I've heard that going to happen this season. I'm not sure when it will happen but I have heard that it will." Source: Kristin on E!Online
08/24 - It will be revealed that Jack has met one of "The Others" back in the real world; this will relate to why he is the only one they are able to cooperate with, although he will be extremely wary in the beginning. Get ready for politics-on-the-beach when the clique returns Jack-less and limping to confront a populace ready for regime change, and an aggressive new leader with a dangerous motivation. Source: The Tail Section
08/09 - Nikki and she'll be a love interest for Rodrigo Santoro<'s character>. Source: Ask Ausiello @ TV Guide
08/07 - Jack, Kate and Sawyer open the season in captivity as prisoners of "The Others." Just who these "Others" are and what they want are primary questions Season Three will explore. Michael Emerson joins the regular cast in his ongoing role as Henry Gale, leader of "The Others." Romance looms on the horizon as Jack's interests veer towards a mysterious new woman, whose motives may be questionable. Sun and Jin will continue to celebrate their pregnancy - but is the child really Jin's? Locke and Sayid will band together with some of the other survivors and journey across the island in an attempt to free Jack, Kate and Sawyer. Charlie will attempt to return into the good graces of Claire and her baby, Aaron, but can he be trusted to stay clean and sober? The fates of Locke, Desmond and Mr. Eko in the aftermath of the implosion of the hatch are answered. Will Penny Widmore find the island and her long, lost love, Desmond, and can the survivors find a way to interact with the outside world? The band of friends, family, enemies and strangers must continue to work together against the cruel weather and harsh terrain if they want to stay alive. But as they have discovered during their 60-plus days on the island, danger and mystery loom behind every corner, and those they thought could be trusted may turn against them. Even heroes have secrets. "Lost" stars Adewale Akinnuoye-Agbaje as Mr. Eko, Naveen Andrews as Sayid, Henry Ian Cusick as Desmond, Emilie de Ravin as Claire, Michael Emerson as Henry Gale, Matthew Fox as Jack, Jorge Garcia as Hurley, Josh Holloway as Sawyer, Daniel Dae Kim as Jin, Yunjin Kim as Sun, Evangeline Lilly as Kate, Elizabeth Mitchell as Juliet, Dominic Monaghan as Charlie and Terry O'Quinn as Locke. Source: ABC
08/06 - It looks like Sanchez closed the deal late Friday , although I have yet to receive an official confirmation from ABC. Source: The Ausiello Report
07/30 - Cusick <...> said: "I've been asked to be a regular for at least a year." Source: The Sunday Mail
07/29 - Elizabeth Mitchell has joined the cast of ABC's hit drama "Lost" as a possible new love interest for Matthew Fox's character, sources said. Source: Yahoo!
07/26 - Rodrigo Santoro, best known to American audiences as the hot dude Laura Linney crushed on in Love Actually, is joining the cast this fall. Source: The Ausiello Report
07/22 - Among the revelations to come: Viewers will learn more about Desmond and Penny, why Locke was paralyzed, why Libby was in the asylum, and why the island has healing powers. Source: Sci Fi Wire
07/22 - The smoke monster is definitely not made of nanobots. Kate will "make her choice" in the first six episodes of the season. Her choice is presumably between Sawyer and Jack. The word "clone" will never be heard on the show. The Powers That Be all but confirmed Libby will be appearing in flashbacks, most logically Desmond's or Hurley's. If you're asking about daddy issues, you're asking the right questions. Strong implication that an underwater hatch might exist and that it might be explored this season. The producers say the hieroglyphics on the timer translate to "underworld". Source: Kristin on E!Online
07/21 - During an interview Carlton Cuse revealed: We almost view the first six as a miniseries. And it's going to answer what we left hanging at the end of the finale. Obviously, we're going to explain what happened to Locke and Desmond and Eko, and sort of deal with the fact that Sawyer and Kate and Jack are in captivity. We would love to sort of finish up 's story. We're casting two female roles and one new male role. I can't tell you where the characters are going to come from, but obviously, one of the things we're doing this year on the show is... learning a lot more about the Others, and their society and their history. So it might be fair to say that you're going to learn more about some other characters who are also Others. I wouldn't call it the season of sex, but I will say that romance will play a much more active part of the show this year... We actually meant to get to it last year. We didn't really get to the romance as fast as we thought we were going to. So this year that's definitely on our agenda. I think actually one of these new female characters is going to be a romantic interest, possibly for Jack. There will be several new romances on the show this year... I think that this year we're looking to make the show a little bit brighter, a little bit more vibrant, a little bit more on the action-adventure axis, a little bit more on the romance axis. I don't think the show will be as dark and as intense this year . And it will be, I think, even more on the character axis than on the mythological axis. John Locke will be a very different person in Season 3. All of his questions and his doubts and his uncertainty have been answered. In fact, the button did mean something. And there was something at stake. And I think that will bring about a change in that character. Penny is an important character in the overarching mythology of the show. The interrelationship between the outside world and the island will be something that will be a part of Season 3. The monster will be a part of Season 3, as will the polar bear. People are asking what happened to the polar bear, so we will be doing some polar-bear stories. The smoke creature and the monster are one and the same. I hope Cindy shows up at some point. Let's just say we have many actors on our show; she is not at the top of the list of actors we're servicing. Source: The Ausiello Report
07/14 - Juliet, a woman in her mid-30s, will be added to the cast as a regular. Juliet is a natural leader and a smart and independant woman. One of her flashbacks (?) will involve her mother Amelia. During said flashback, the ladies will discuss burnt brownies and Juliet's love life. It seems that Juliet may be an Other. Jack is held alone in a room and Juliet looks at him, separated from him with a glass window. Jack tries to break the chains that are holding him. Juliet tries to convince a pissed off Jack to trust her. Source: SpoilerFix.com
06/12/2006 - I *believe* Locke, Eko and Desmon will be back. Terry O'Quinn and SexAAA (Adewale Akinnuoye Agbaje) are both under contract, and I've heard Desmond will be back. Now, that could be in a flashback, but it was my understanding his next appearance would be more of the still-breathing-on-the-island variety. Source: Kristin on E!Online
05/29/2006 - Summary of spoilers given by Damon Lindelof and Carlton Cuse: Next season, we will understand the real ramifications of Desmond activating the failsafe and what that did. The central issue of season three will be what did happen. It sounds like Desmond's coming back. They said they want him back, we want to know why he was in prison, we want to know what happened when he turned that key that affected the entire island. That will become very important. The island was visible but only for an instant. It was also visible for an instant on 9/22/04 when the plane crashed. The foot statue represents the history and archeology of the island. Season three will explore what happened on the island before Dharma arrived in the late 70's and who was there. The smoke monster will definitely be back in Season three. There is a good chance we saw the monster this year and didn't realize we were looking at it. By the end of next year we will realize what it was and when we saw it. Why did the Others take Jack, Kate and Sawyer? Where is their home? That will be the story told over the first six episodes. Season 3 will also be about the main characters and their relationships. They want to service the relationships next year more than the mythology. How Locke got in the wheelchair, how Jack got his tattoos will be revealed in Season three. Source: Lost Podcast
05/26/2006 - I just received some exclusive intel on the new characters joining Lost. In addition to the two female roles, the show is also adding a new hunk. Descriptions are: Female, 30s, with leadership qualities. Female, early 20s, very attractive. Male, Latino, early 20s, handsome, mysterious quality. My guess? These are some of the "background" survivors that Carlton Cuse told me would emerge next season. Source: The Ausiello Report
05/26/2006 - Next season will be about the Others, as led by the oblique Henry Gale (played by Michael Emerson, who will join the regular cast). Mr. Cuse listed what viewers will learn about the Others by this time next year: "Who are these people? How many of them are there? What is their history? What are they trying to accomplish?" Source: New York Times
05/25/2006 - Producers of ABC's hit series Lost <...> told SCI FI Wire that it sets up the upcoming third season, which will focus more on romance—and on the mysterious Others. "The Others are an important part of season three, and there's a lot of mysteries and a lot of questions about the Others that the audience is going to be curious about going into season three," said executive producer Carlton Cuse in an interview. "And those are the things we're going to explore." Cuse added: "There will definitely be some new characters on the show next year... Obviously, Michael Emerson, who plays Henry Gale, he's someone who's going to be very prominent in the show next year." Fans were also introduced to a new character who promises to figure in next season's storylines: Penelope Widmore, played by Sonya Walger. <...> "I'm excited about love in season three," said executive producer Bryan Burk, adding: "Don't forget now the people have been on the island for 60-plus days. They're now obviously more familiar with each other... The concept of love is there, and... it weaves its way through all of our characters. It's going to be much more prevalent in season three." Source: Sci Fi Wire
05/24/2006 - Carlton Cuse reveals: I will say that the next season is a lot about the Others. There's a lot of mysteries about the Others that we'll be getting into next year. Source: E! Online
05/24/2006 - According to the Hollywood Reporter, ABC's Lost is on the hunt for two new actresses to join the cast for Season 3, now that the show's distaff ranks have been quickly depleted by the twin killings of Michelle Rodriguez's Ana Lucia and Cynthia Watros' Libby. Source: TV Guide Online
05/24/2006 - slim to none, according to Carlton . "Never say never, but we feel like we told her story," he reveals. "Her arc had a beginning, middle and an end." "You will find out what happened to Cindy," Source: Ask Ausiello @ TV Guide
05/22/2006 - Harold Perrineau is not a regular for next season. He could be back as a guest star (à la Walt this season) but not as a regular cast member. Source: Kristin on E!Online
05/17/2006 - Michael Emerson (Henry Gale) <...> is returning next season as a series regular.Source: The Ausiello Report
05/16/2006 - there will be new locations and new characters (one rumor has Desmond joining the cast full-time, but producers won't comment). The season's big theme sounds timely, twisty, and terrifying. Hints Lindelof: "'Us versus Them.' But who's the 'us,' and who's the 'them'?" Source: Entertainment Weekly
05/14/2006 - Damon Lindelof : Libby's got this mysterious backstory, of which we've only given you the tip of the iceberg. We know she's spent some time in the mental institution with Hurley, and the idea of killing her before she had an opportunity to explain how she got there... we have a master plan for how we're going to tell that story, but it's all posthumous. You'll start to learn Libby's moves through flashbacks over the course of the next season. So we're not done with Cynthia, but Libby is dead. Source: The Ausiello Report
05/03/2006 - Lindelof & Cuse: The growth of Malcolm David Kelly (Walt) will be addressed in the 3rd season. You can expect to see more of Rousseau next year, but the story of the wrecked research vessel, it will be coming at some point but we can't guarantee it'll be in Season 3. We'll be introducing new characters in Season 3, so you'll be getting fresh flashbacks. You'll probably see fewer flashbacks of our original characters as we begin to move toward certain inevitabilities. You will learn more about some of the other survivors next year. Also, where the new characters come from in Season 3 is going be part of the fun and anticipation over the summer, and hopefully by the end of the finale you'll be getting some sense of who those characters might be. We are going to produce the next 22 hours of Lost in Season 3. Source: Ask Ausiello @ TV Guide
11/28/2005 - Writer/Supervising producer Javier Grillo-Marxuach reveals (note that this is a summary of the spoilerish things he revealed): You have not seen the last of Dharma, but it's going to be a little while before you find out a little bit more. The Dharma Initiative was a communal research facility on the island. A lot of scientists and free-thinkers got together to do a lot of different kinds of research: psychiatry, zoology - and remember that with the zoology of the film you saw some polar bears. It's possible there were some animal aggression studies going on there, as well as human psychology experiments and a whole variety of other things. The Dharma Initiative was founded by two peacenik Grad students who were trying to get to the bottom of a lot of mysteries about human behavior. There are six bunkers on the island, and they were devoted to a lot of different kinds of research. That's going to open up a lot of different avenues for us to tease you with what the kind of research was, and how it's evolved now that the Dharma Initiative seems to have fallen into disrepair. A lot has happened on the island and the Dharma Initiative is just the tip of the iceberg... Source: The Official Lost Magazine, Issue 2, Jan/Feb 2006
09/19/2005 - From Damon Lindelof: There is going to be a flashback story that fully explains the significance of all tattoos and puts it into the framework of what was happening in his life when he got them. Source: Kristin on E!Online