from wikipedia:
The survivors are dead and/or in Purgatory — dismissed by J. J. Abrams [24]
The survivors are in a time warp — dismissed by Damon Lindelof [25]
Spaceships or aliens influence the events on the island — dismissed by Damon Lindelof [25]
Everything seen is a fictional reality taking place in one or more of the survivors' minds — dismissed by Damon Lindelof [26]
The island is a reality TV show and the castaways unwitting housemates — dismissed by Carlton Cuse [27]
The "black smoke" is a nanobot cloud similar to the one featured in Michael Crichton's novel Prey — dismissed by Damon Lindelof [28] [29]
http://en.wikipedia.org/wiki/Lost_(T...dited_theories
oh, the nanobot one is a new addition. ok, scratch that off my list.