The Power of Now: A Guide to Spiritual Enlightenment - Eckhart Tolle

Don't even think about it, just get this book. Even if you are advanced in spirituality, even if you are a total non-believer, I think this will change your life. It's like it opens your eyes and you see completely differently. It's amazing. By the way, I highly recommend listening to it while you're hiking or walking around in public. It brings everything to life!