I knew there was one I was forgetting, A Brief History Of Time, By Stephen Hawking.
First of all, this man is brilliant, easily the smartest man alive (he is widely regarded as just such), and possibly the smartest man ever.
Second, the book tackles such vast topics as the very nature and creation of time and space.
Third, for all those who have been on the thread regarding the existence of god, this book addresses all the topics with regards to god, from a neutral point of view.
Finally, while this man is a brilliant physicist, and almost everything he discusses involves very advanced science, it is written in such a way that even a laymans can understand