The Secular Web
Contains many articles about atheism. Plus a blog and discussion forum.
http://www.infidels.org/

Famous Dead Nontheists
A listing of famous atheists, each with a brief biography.
http://www.jmarkgilbert.com/atheists.html

Are God and Ethics Inseparable or Incompatible?
An article discussing the moral argument for God and the counterargument for atheism.
http://hem.passagen.se/nicb/god_ethics.htm

Morality Without God
An essay which discusses whether morality is evidence of God.
http://www.spectacle.org/1095/moral.html

Ethical Atheist
Group resisting the influence of religion while promoting a scientific and nonreligious worldview.
http://www.ethicalatheist.com/

Dave's Things To Think About
Provides a collection of essays about contemporary theological issues from a sceptical perspective.
http://users.rcn.com/davestul/things.html

Atheism and Agnosticism
Looks at the similarities and differences between atheism and agnosticism.
http://plato.stanford.edu/entries/atheism-agnosticism/

BBC: Atheism
An introduction on the history, rituals, and different types of atheism.
http://www.bbc.co.uk/religion/religions/atheism/

Wikipedia: Atheism
Online encyclopedia details the history of atheism, the different types, and how it relates to the religions of the World.
http://en.wikipedia.org/wiki/Atheism

Wasteland of Wonders: Atheism
Articles about atheism, humanism, and skepticism.
http://www.abarnett.demon.co.uk/atheism/

Atheism
Provides proofs that atheism is invalid. Also has tips on how Christians and atheists should communicate.
http://www.carm.org/atheism.htm