National Library of Medicine
The world's largest medical library. It collects materials in all major areas of the health sciences and to a lesser degree in such areas as chemistry, physics, botany and zoology. http://www.nlm.nih.gov/
Spine Health
In-depth information about back pain and neck pain, including causes, symptoms, diagnosis and full range of treatment options. Written by spine specialists. http://www.spine-health.com
BackCare
UK charity offering advice on how to care for your back. Some good information on self care. http://www.backpain.org