I have been watching Lost since the 4th episode of Season 1. I am one of those guys who re-watches every episode numerous time in-search for any little clue that may lead to the ultimate theory explaining everything from the smoke monster to the statue. I have several theories concerning Lost, but I decided to post some of my favorite theories form my favorite Lost blog, Dark UFO. So please enjoy, and hopefully these will lead you to new ideas and conclusions about the show.
Also, as an honorable mention, I must post one of the most discussed theories in existence. While I think most of this can be debunked based on recent events, this is one of the most detailed and thorough theories for its time (it was written around the time of season two). It come form the popular forum 4815162342. This may take awhile to read, so grab a Dharma beer and relax.