Stackoverflow is a niche site, but for its niche it is absolutely amazing. The site features a tremendous community of developers who ask and respond to questions. This creates both a huge knowledge base of existing information and a quick way to get additional information. It is very similar in concept to
Aardvark or Yahoo! Answers but differentiates itself in its tight focus on development related topics. If you are a developer or are considering becoming one this site is an absolute must.
If you do sign up – say hi – I’m davemackey on stackoverflow. 🙂