Health

Consumer Health

AMA Physician Select
HealthWeb
Medical Library Association
MedicineNet.com
Merck.com: online medical manuals.
National Library of Medicine
WebMd.com

Nutrition

Dietary Guidelines for Americans
Food Guide Pyramid Information
National Institute of Health Office of Dietary Supplements

Specific Disorders

Cancer.gov
Centers for Disease Control
CIDRAP (Center for Infectious Disease and Policy)
POPline: Reproductive health literature.

Environment and Statistics

EPA Publications
National Center for Health Statistics
National Safety Council
Scorecard: Provides local environmental information by zip code.

Pharmaceuticals

RxList