Jason Kottke points to Memory Alpha, a 8200+ page fan encylopedia of the Star Trek Universe. This is absolutely brilliant — as Jason points out, a perfect use for a wiki. It appears to be running on the MediaWiki engine.
Memory Alpha has a following disclaimer in its footer: "Star Trek and related names are trademarks of Paramount Pictures, and are used under "fair use" guidelines." I doubt if this really qualifies as fair use, and I imagine that if Paramount wanted to come after them, they could. I hope they don't, because as Ron Moore points out, with Enterprise canceled and no new series or movies in the works, Star Trek is (for now) in the hands of the fans. And I think that's a good place for it to be.