http://www.infidels.org
A web site chock fill of information that counters arguments for the existence of god, and provides many uncountered arguments against his existence. Also covers some other major religions, such as Islam, Judiasm, and Hinduism. Most articles are focused on Christianity, however.
Contains a wide variety of writers, including many who were quite involved with religion previously in their lives, such as a number who were ministers/pastors. Contains book reviews of many books for and against various religions, and a number of articles that refute arguments in popular books for religion.