This was another no-brainer. It's also another book, but I don't think I'm alone in saying that it's probably the greatest non-fiction work to be found.
My greatest treasure is my Bible. In today's society, it might hard to think of something so widely distributed and easily available as The Bible as something to be treasured. However, this book is the divine word of God (reason enough to treasure it), and the rope that ties me to my Anchor- Jesus Christ: it is also a treasure because I know that this book- so easily procured for us- is an item much sought-after and yearned for by others far less fortunate than I. It is still not uncommon to hear tales of poor and needy people in other countries working for many years and going long distances to obtain one of these. I am truly blessed to have it, and am even more blessed to be able to practice my faith openly, and without fear of oppression.