Drug and Alcohol Abuse
National Clearinghouse for Alcohol and Drug Information 
ClubDrugs.org
Drug Facts  
HIV.drugabuse.gov  
National Institute on Drug Abuse   
Smoking.drugabuse.gov  
SteroidAbuse.org  
Teens.drugabuse.gov   
Health Information: Nicotine Addiction

Fitness
American Heart Association 
Fitness on Yahoo
Healthier U.S.-Gov.
Sport Fitness Advisor

HIV/AIDS
AIDSInfo
The Body: A Multimedia AIDS and HIV Resource
HIV/AIDS: Center for Disease Control
HIV InSite UN AIDS

General Resources
Centers for Disease Control and Prevention, especially CDC Health Topics - A to Z 
Department of Health & Human Services
Healthfinder.gov
InteliHealth
National Center for Health Statistics
National Institutes of Health (NIH)  
Science Magazine
TeensHealth
WebMD 
WHO/OMS: World Health Organization
Go Ask Alice!
Scientific American
Wolfram Alpha - Health and Nutrition Computations

Medicine
Informed Health 
Mayo Health Oasis: Daily News on Disease
Medline Plus
Medscape
National Center for Complementary and Alternative Medicine
PubMed
Medical Animation Library

Mental Health
Substance Abuse and Mental Health Services Administration (SAMHSA)
Mental Health America
Mental Help Net
National Alliance for the Mentally Ill
National Institute of Mental Health
Psych Central

Nutrition
Food and Nutrition Information Center - USDA
Food Timeline
Shape Up America!

Sex and STDs
I Wanna Know
Sexual Health
Teenwire