AllRefer.com
A virtual medical encyclopedia offering "extensive information on over 4000 topics arranged in an A-Z order". It is not only extensive but offers easy to navigate pathways and guides to symptoms, diseases, diet & nutrution, health news and more.
BioMedSearch.com
A huge and constantly expanding database for all things health/medicine related. "BioMedSearch is a biomedical search engine that contains NIH/PubMed documents, a large collection of theses, dissertations, and other proprietary publications not found anywhere else for free, making it one of the most comprehensive and powerful free biomedical searches."
Healthy Lifestyle
From the Mayo Clinic, "Information and tools for a healthy lifestyle."
Shape Up America!
Created by former US Surgeon General C.Everett Koop, an online fitness center which offers diagnosis and fitness plans customized to individuals who complete a brief questionnaire. Includes practical suggestions for exercise and diet.
Medicine & Medication
Clinical Trials
A "clinical trial listings service" from Centerwatch. Resources for patients and health professionals.
Merck Manual
The centennial edition of this respected manual "dedicated to providing reliable, easy-to-use medical information".
RxList
"The Internet Drug List". Created by a pharmacist. Features search tools, current drug information, and more. (Sadly, they've recently lost their very good comix page - all biz now.)