Mercola
A fantastic site, with a HUGE amount of diet and other holistic health-related information. Dr Joseph Mercola is a medical doctor with an passion for natural healing methods, and I recommend his site (and newsletter) very highly.
Weston A Price Foundation
Weston Price was a prominent dentist who spend years of his life researching traditional natural diets and their impact on health. His foundation continues his work today, and this site provides a wealth of information on their findings.