Bogleheads.org is a website for mutual fund 'enthusiasts'. Bogleheads emphasize regular saving, broad diversification, and sticking to one's investment plan regardless of market conditions. Information relevant to the group's core beliefs is available in The Twelve Pillars of Wisdom and Vanguard's Investment Philosophy.
The forum's regular posters discuss financial news and theory, while also helping less experienced investors develop their portfolios.
Wiki:
http://www.bogleheads.org/wiki/index.php/The_Bogleheads
Forum:
http://www.bogleheads.org/forum/index.php
