Probably required reading if you are interested in the intersection of religion and science. I admit that Dawkin's style can come off as overbearing at times, but he makes excellent points. Whether or not you are an atheist, you should read this. 
 Spoiler Alert! Dawkin's conclusion is that religion is basically a mental virus that piggybacks on our hard-wired tendency to obey our parents and have imaginary friends as children.