The Prize - Daniel Yergin.
Siddhartha - Herman Hesse
The first is a fantastic history of oil. It brings out the politics, economics and personalities that have lit up the history of oil very well. Especially relevant in this day and age, when oil is behind so many geo-political conflicts.
The second is a bit more personal. I could write an entire essay about this book, but suffice it to say that it was exactly the right book at the right time for me. Sometimes, a book just comes along and changes your perspective and way of thinking. This was one of those books for me.