To extend Brian's list slightly, I would also recommend these websites:
the excellent and comprehensive jesusneverexisted.com;
atheist-experience.com (plus there's tons of their videos on YouTube);
ironchariots.org, the Atheist Experience's own wiki;
rationalwiki.org;
and if you're in need of a laugh, or just want to despair for humanity:
Fundies Say The Darndest Things (fstdt.net)
the excellent and comprehensive jesusneverexisted.com;
atheist-experience.com (plus there's tons of their videos on YouTube);
ironchariots.org, the Atheist Experience's own wiki;
rationalwiki.org;
and if you're in need of a laugh, or just want to despair for humanity:
Fundies Say The Darndest Things (fstdt.net)
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'