Less Wrong
“Less Wrong is an online community for discussion of rationality. Topics of interest include decision theory, philosophy, self-improvement, cognitive science, psychology, artificial intelligence, game theory, metamathematics, logic, evolutionary psychology, economics, and the far future.”
I linked to an interesting article from Less Wrong earlier today that made its rounds on Hacker News yesterday, and spent some time browsing the site throughout the rest of the afternoon. I have already saved a number of articles to Instapaper, and look forward to spending a fair amount of time on the site in the near future.