The God Delusion by Richard Dawkins

It has resulted in my ordering his "The Selfish Gene"

if you ever wonder why we are here, or what it is all about, then his stance that we are carriers for genes to spread themselves makes sense and answers a good few questions.

Also puts superstition into perspective.

It's just a pity that he harps on and on so much he is rather irritating when on the radio / telly or being quoted in newspapers.