I agree with many of the books recomended here.
I really loved Autobiography of a Yogi which is now free to read on the net.
Click Here
Its the story of the man who brought yoga to the west.
I also love The Power of Now, and am just about to start A New Earth.
While I'm here I just like to point out the first book I ever read which took me down a more spiritual way of thinking.
A Souls Journey by Peter Richelieu
Amazon.com: A Soul's Journey (Classics of Personal Development): Books: Peter Richelieu