The God Delusion - Richard Dawkins

In comparison with The Hitch, Dawkins is the sober and reasonable face of the current surge of atheist pamphleteering. I would actually recommend this book to a curious reader because, whilst not as much fun as God Is Not Great, it is more structured and persuasive.

The God Delusion occasionally gets bogged down in the author's pet subject of genetics, but the argument is strong and some of the asides and footnotes are delightful.