I don't think atheists exist, and I'll tell you why.
To my understanding, some "god" or "gods" appear in every world religion (actually, I think maybe Buddhism is the exception, although I am not a scholar of Buddhism). God is generally thought of as all-powerful, the creator of everything we see around us, the ultimate source of moral guidelines, etc. I think atheists do believe in a god, and I think each of them knows that god's name. Let's examine those "god" identifiers, which I just came up with off the top of my head, in some detail:
All-powerful: Atheists do not believe in one all-powerful being. However, if you asked 100 atheists who is responsible for what happens to human beings, atheists would answer, "themselves." (Or maybe, "chance.")
Creator of everything: On the subject of origins, there is very little choice for atheists but the rickety contraption we refer to as "evolution."
Ultimate source of moral guidelines: The only choices here would be that each individual is responsible for his own morality, or maybe the laws of government or some other body. I suppose you could say that humans have a sense of morality built in, but if you say that you have to presuppose a builder, which an atheist would not do.
Do you see the common thread here? Who makes everything happen? "Human beings." Who created everything? "The human race created itself through the process of evolution." Who is the source of morality? "Human moral codes." In all cases, the finger that should point at God, points at HUMANITY.
I don't believe in atheists. I do believe in and respect agnostics, who at least are honest and brave enough to say "I don't know," but other than that, everyone believes in a god; you can't be "a-" ("not-") theist. For one thing, it is impossible to disprove an intangible "spirit" entity. But more importantly, "atheists" actually ascribe all of the characteristics of "god" to themselves. What does that make them... "me-theists?"
Update: I don't believe in atheists II