Boy, if anything needed a wiki, it’s Lost. Like most of the Internet, this site is severely compromised at the moment due to April Fools’ garbage–don’t believe anything you read on the home page for the next few days–Google didn’t buy it, all will not be revealed in the next episode–but generally this is a fun resource. Definitely don’t look at it if you aren’t caught up, though, because it’s spoilers on top of spoilers (and spoilers all the way down). If you are caught up, this is your chance to see what all that crap on the blast door was.
Specific to my own interests… the Terry O’Quinn page isn’t great, but then there’s not a lot known about the guy. Naturally the John Locke page is more developed.