NHS Health A - Z
A wealth of health advice, as you would expect.
NICE
The National Institute for Health and Care Excellence has evidence-based reviews, specialists libraries, books, journals.....Huge. Some access may be limited to NHS staff.
Spine-health.com
An American site with a detailed description of the anatomy of the spine and a more technical explanation of the conditions that can cause back and neck pain.
Patient UK
Like asking your GP for health information, but without the wait in the surgery.