Stackoverflow is a newish service for developers - ask a question, get answers, vote on answers, build reputation. Sort of like Yahoo! Answers but for developers.
I'm surprised at how good the service is so far. I asked a question on IRC and the same question on Stackoverflow. Within 2 minutes I got an incorrect answer on IRC and the two correct answers on Stackoverflow. The voting and reputation seems to really work and there's no IRC trolls / egos to deal with.
I'm hoping the site will maintain its usefulness as it grows. Well worth checking out. I'm here.