I recently read Work Out: The Revolutionary Method of Creating a Sound Body to Create a Sound Mind By Dr. Jason Karp which provides good motivation to exercise, with plenty of scientific evidence for its health benefits. Dr. Karp, who has a PhD in Exercise Physiology, especially emphasizes the importance of exercise for mental health. He believes that various higher brain functions evolved to support our ability to do physical activity, so exercise is crucial to keep our brains healthy. There are various areas in which it has been shown to help. For example, exercise is superior to medications in alleviating depression, and it helps stave off cognitive decline. The first part of the book is devoted to inspiration and scientific evidence, while the remainder gives a complete guide to both cardiovascular and strength training. I found this to be a very useful book.