MedlinePlus
http://www.nlm.nih.gov/medlineplus/
A wide range of topics for any age. 

FamilyDoctor.org
http://familydoctor.org/online/famdocen/home.html
Family health topics, including a guide to OTC drug; large print and Spanish available

Cancer.gov
http://www.cancer.gov/
Information on all cancers and clinical trials pertaining to treatment.

HIH Senior Health
http://nihseniorhealth.gov/
Topics for seniors with options for large text and read-aloud text.

Medicinenet.com
http://www.medicinenet.com/script/main/hp.asp
Slide shows containing pictures and information on a wide range of topics.

KidsHealth.org
http://kidshealth.org/
Information on diseases, anatomy and health issues geared toward kids.

HealthFinder.gov
http://healthfinder.gov/
Current health news and prevention tips, also an expansive drug interactor finder.