In advance of the season 3 premiere (Oct 4th), Blogcritics.org has put together a list based on *ahem* extensive research on the web and from what little info ABC has leaked. Proceed with caution.
Episode 6 of Season 3 is the "fall finale" since no new episodes will be aired until February 2007. The lost producers say that the first 6 episodes of season 3 form a mini story arc. Here's some speculation and spoilers about the fall finale.