I'm enjoying answering questions on StackOverflow; after getting so much help from the site, I wanted to give a bit back.
I'm finding I'm learning just as much as I'm answering, which is very rewarding.
Q&A for professional and enthusiast programmers
Q&A for meta-discussion of the Stack Exchange family of Q&A websites
Q&A for professional programmers interested in conceptual questions about software development
Q&A for user experience researchers and experts
Q&A for computer enthusiasts and power users
Q&A for science fiction and fantasy enthusiasts