A friend gave me her copy of this book a few years ago, and it completely changed the way I take care of my back. http://www.amazon.com/Treat-Your-Back-Robin-McKenzie/dp/0959774661
For many years, I had chronic low-grade back pain with occasional bouts of complete incapacitation from muscle spasms, but the exercises here (and really, just the way it taught me to think about how I sit and lay down) have made it so that I barely have back trouble at all. I hike and do step and Zumba now with barely any problems. I know, I sound like a shill, but it really made a huge difference for me and now I recommend it to everyone.