Born to Run: I would have to suggest this book to anyone who is an avid runner, or looking to get into it.  Or even if you just like a good story or anthropological study.  This book looks at a tribe of runners in Mexico called the Tarahumara Indians who can run unfathomable distances (over 100 miles) without a second thought.  He compares them to the best Ultra-Distance runners in the states and finds that they have the same running technique and style.  It has changed the way I run, and I have been injury free since.