I'll make a suggestion that is somewhat odd for HN since it is effectively poetry:

The Prophet by Kahlil Gibran

This little book stumbles into my life every 5 or 10 years and always reinvigorates my appreciation for the beauty of life. It is like being swept away by a beautiful piece of music - it can touch your soul. Then again, like music, it is not for everyone nor even repeatable for yourself depending on what mood you are in.