I believe Richard Dawkins is one of the smartest and most rational people of our time. His latest book "The God Delusion" is fantastic. It's an a well thought out and clear exploration into why "god almost certainly doesn't exist". It's a great read and I highly recommend it for the religious and secular alike. Everyone can walk away with something positive from the experience of reading this book.

He also pretty rationally exposes why even if god does exist, why it doesn't really matter. What we need to do is worry about getting along in this life and taking care of each other rather than worrying about punishment or reward after we die.