List of communities
Communities which may be useful to aspiring rationalists. Changes may be suggested in this comments thread or edited directly. You might want to track the current state of the diaspora also.
General
Change my view - place to get your view challenged
Rationality
The Akrasia category of the Beeminder forum
Skeptics
Skeptics Stack Exchange - useful for confirming factual claims you are skeptical of. Requires specific, answerable questions
Straight dope - similar to Skeptics, but less strict on the questions accepted
QA Sites
Stacks: StackOverflow, Computer Science StackExchange, Theoretical computer science, MathOverflow, Math StackExchange, Cross Validated, Physics Stackexchange
Cognitive Science - you are expected to do your reading first, but useful if your want to lean about what the research says