The God Delusion (buy from Amazon) by Richard Dawkins
A very deep and comprehensive book that talks about why there is no God, not an easy book to read. "God delusion" covers a very wide angle, "Respects that religion doesn't deserve", "God Hypothesis", Why human is receptive to the idea of religion and how religion arised as a result, the inconsistency in scriptures people simply choose to ignore, the alternatives to God that can still explain the world, the human moral standard with or without God, Science Vs Religion. Dawkins is a firm believer in Evolution/Darwinian world.
I have enjoyed reading this book very much, it will help you to decide one way or the other.