Healthfinder.gov
Sponsored by U.S. Department of Health and Human Services. Offers quick links to 1600 health topics. Non-biased information. Also includes "health news" section, guide to local services, and personal health tools and risk calculators.

Medlineplus.gov
Maintained by the U.S. National Library of Medicine and the National Institute of Health. Easy to navigate, abundant with unbiased information. Superb in how it grades the weight of scientific evidence supporting various claims.

Mayoclinic.org
Has a substantial directory of disease topics, sections on tests and procedures, symptoms, drugs.
Not a great deal of depth on any topic, but quick and easy to navigate.

Uptodate.com/patients
Extremely reliable and accurate information, kept very up to date. Provides a condensed version of articles on broad range of topics. Access to the professional level (much more sophisticated discussion) can be purchased for $20 for one week access or $45 for one month.

Merck.com/mmhe
The electronic home edition of the Merck Manual. While not "up to the minute" current on new thinking and treatments, it is nonetheless a well-written general medical textbook covering bread-and-butter basics. Print version has been a staple on doctors’ shelves for decades – amazing to see it free on-line. Good section on older adult health.

Consumerreports.org/health
Health website maintained by Consumer Reports Magazine. It appears like you need to subscribe, but actually offers some quality information free if you dig here.

Americanheart.org
Great organization, great site. Here is what you must know about heart, blood pressure, cholesterol, stroke, peripheral artery disease, diabetes. A trove of information.

ACPonline.org
Website of the American College of Physicians (internal medicine physicians). Click on "Patients and Families" (button on top right of screen). Excellent patient education videos and free downloadable brochures.