By far my favorite book is seven habits of highly effective people. The reason I like it so much is because it deals with the fundamentals and does it very very well. It offers the most balanced approach I have seen so far. Its focus is character development, that is: building your free will, your ability to plan and follow through, your integrity, your ability to understand other people's point of view. I'm through my third paperback version and I'm going to buy it as a hardcover now.
It's also available as an audio version, which I, naturally, own, too and can also recommend.
Second place would be Og Mandino's "The biggest secret in the world" (just ignore the cheesy title
)which follows a similar approach and is more action-focused but less philosophical. It helped me a lot, though.