I'll pitch in a few sites I like:Hunch
It's sort of a recommendation system based off your tastes. You sign up, fill out a series of random questions, and then it determines things you're likely to like from the "taste" profile you created. The more questions you answer, the more it learns about your taste in just about anything.
Pretty cool site. I find it most useful for book recommendations.Quora
It's like Yahoo Answers, with actual intelligent life forms responding to the questions (for the most part).Qwiki
It's "visual" Wikipedia. I don't think it's that useful yet, but I like the presentations and there's a lot of potential for this kind of site. It's in alpha stage, so plenty of room for growth.