Atheism:

American Atheists

Atheism/Agnosticism 'About' group w/live chat, links, articles, etc.

Atheist Alliance

Atheist links -- New website!

Celebrity Atheists

Infidel Guy - atheist radio show

Positive Atheism

Links by topic:

Humanism
Secularism/Freethought
Science
Religion
Atheism
General Interest