I just ran accross this site, and it is fantastic.
"I am an atheist.
And no, I don't kick puppies or steal candy from babies. I don't hate God, but I don't have any secret desire to worship him either. Nor do I worship Satan. I'm not angry or depressed; I'm quite happy as I am, actually. In fact, I'm a person just like you. You probably wouldn't recognize me if you passed me on the street.
But I am indeed an atheist. What this means, quite simply, is that I don't believe in any gods. Not Jesus, not Yahweh, not Allah, not Vishnu, not Odin, not Zeus, not Gaea, not Quetzalcoatl, not Marduk, not Ahura Mazda, nor any other of the thousands and thousands of deities humanity has invented throughout its history. I don't single out any of them - I treat them all the same, and lack belief in each one equally. As far as I'm concerned, they're all imaginary - mere products of the human imagination and nothing more.
In this respect, I'm probably not that different from you. After all, most theists reject all but one of the many gods humans have invented. I just reject one more god than most people do."
If anyone wants to learn more about why atheists don't believe in God, and really what being a nonbeliever is all about, I can't think of a more well-considered place to do it. I'm already an atheist and I could while away the entire afternoon between the atheism and evolution pages.