It would seem that the word on the grapevine is that a good few members of the original Lost cast might be returning, even from the grave, for season 6.
After the events of 'The Incident' in season 5's finale it looks like time will be resetting itself and that Oceanic flight 815 might be back on track on its original flight path from Australia to LA with it original passengers intact... Maggie Grace is going back to Hawaii to do some secret shooting and the whispers are that Charlie (Dominic Monaghan) is coming back too. No word on Michael and Walt (no idea how they'd bring Walt back when he's so much older and taller now) or any others from the original first and second season, but at least we know for sure that Claire (Emilie de Ravin) will be returning with a very important storyline...
I'm sure the creators will attempt to get at least a fair amount of cameo's for the original cast who were passengers on the original flight, even if it's stock footage from previous seasons, just so we have some continuity and 'oh cool!' moments. Can't imagine how they'll do next season logistically... Will they make it to LA or will they crash again on the island and start from scratch? And are Jacob and the other guy God and the Devil? Only time will tell!
Can't wait, Lost has redeemed itself this past season into being one of the most watchable shows on T.V.!