American Academy of Family Physicians - Surveys and Statistics, Meetings, Chapters. 
American College of Emergency Physicians - ACEP online, misc. information for ER  Physicians.
American College of Physician Executives - Education, careers, graduate programs, a bookstore and reference links. 
American Gastroenterological Association - Events, Public Policy, Membership,
Gastroenterology News, Publications, Physician/Scientist driven.
American Lung Association of Washington - Working with the mission of preventing lung disease and promoting lung health. Nice and easy to read.
American Medical Association- Physicians dedicated to the health of American.
American Neurological Association - National site, database and membership information.
American Psychiatric Association - Clinical Resources, research resources and public information.
Centers for Disease Control and Prevention - News, travelers health, publications, software and products.
Consumer Information Center - The Pueblo Co. Company, great site.
Delicious Online - Magazine online, Healthy Issues, Recipes, and a health chat.
Emory Eye Center - Professional Group, patient, professional areas.
EyeNet - The American Academy of Ophthalmology Site. Many active issues.
Food and Drug Administration - Information about just about any food product.
Harvard Brain Tissue Resource Center - Info for Pathologists, researchers. Detailed.
Health and Law Policy - Health and Law studies from St. Louis University.
Hospital Web - Listing of US Hospitals
JAMA -  HIV/AIDS Information Center Library, Treatment Centers, Education, Prevention, Healthcare Policies.
Management Professional in Healthcare - Pittsburgh health organization
Mayo Clinic & Foundation for Medical Education and Research- The one and only. Many links to all Mayo areas.
Mayo Health Oasis - The Mayo's health page, info and links.
Merck Manual - You have to fill out the registration but after that you're in. The site looks new but very useable.
National Foundation For Infectious Diseases - National Site and information.
National Health Information Center - Research database and more.
National institute of Diabetes and Digestive and Kidney Disease - Research, databases and more
National Institute on Drug Abuse - Information, publications, stats.
National Organization for Rare Disorders -Search engines, links and programs and services.
The MedExplorer - Great medical search engine.
Transweb: All about Transplantation and Donation 
Whole Brain Atlas - The Harvard Medical School's Site. Explaining the Normal Brain, Strokes, Tumors, Degenerative Diseases, as well as inflammatory or Infectious Diseases.   Detailed info.
Women's Health - General Health Info, Breast Cancer, Reproduction, Do it yourself Breast Exam, Plus many links to other issues important to women's health.
Women's Health Forum - Healthy tips, search are as and more.