The American Chiropractic Association’s website is a good resource for people with back pain. Not surprisingly, there’s an emphasis on the benefits of chiropractic along with a search function for finding a local practitioner, but they also offer very helpful information for back pain sufferers.
Harvard Medical School hosts a great site for people searching for all kinds of health-related information. It includes a lot well-written, non-academic material covering a wide range of topics. Of course, it being Harvard, you can also find a great many research papers and postings for doctors, researchers and healthcare professionals.