If you want to read scholarly refutations of arguments for the existence of God, as well as read some arguments put forward explicitly for the non-existence of God, then you have to turn elsewhere: Michael Martin's "Atheism: A Philosophical Justification", Robin Le Podevin's "Arguing for Atheism" and Nick Everett's "The Non-Existence Of God". Another good book from an agnostic rather than atheist perspective is Anthony Kenny's "The God of the Philosophers". A slightly easier read is Julian Baggini's "Atheism: A Very Short Introduction" which is okay. I have some reservations with it, but it covers most of the important arguments and has some stuff about ethics and living the good life and all that happy-clappy stuff too.
As for stuff that isn't concerned with the philosophical arguments? I found Onfray's "In Defence of Atheism" a pretty good read - it is polemical, but is well-written. Nietzsche is always good to read so long as you don't - you know - become a damn goth or whatever after reading it or try and commit genocide or something. Russell's "Why I Am Not A Christian" and the much less read compilation "Russell on Religion" (not widely available outside academia as far as I'm aware) - Russell is a good writer and says some very refreshing things like:
<blockquote>Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own.</blockquote>
Perhaps the newer
The New Atheism: Taking a Stand for Science and Reason