Library Catalogues and Indexes:
Columbia University Digital Library Collection
Library of Congress Catalogues
Medlars (MEDLINE, HISTLINE, etc.)
National Union Catalogue (manuscripts before 1600)

Digital Collections and Sources:
American Memory Collection (Library of Congress)
Bulletin of the History of Medicine
Case Studies in Environmental Medicine
Five Points Site
How the Other Half Lives (Jacob Riis)
Images of the History of Medicine (NLM)
JSTOR (Selected Journals)
Visible Human Project (NLM)

Databases, Discussion Lists, and Web Guides:
AIDS Daily Summary (CDC)
American Library Association Health Statistics
Biomedical Resources (Yale)
H-Net
History of Race, Science, and Medicine
History of Science, Medicine, and Technology
Local Health Department Web Sites
Med Web
Medical History on the Internet
Statistical Databases (CDC)
Web Sites for Historians (Center for History & New Media)

Libraries and Museums:
Dewitt Stetton, Jr. Museum of Medical Research
National Library of Medicine
National Museum of Health and Medicine
New York Academy of Medicine
New York Public Library
Robert L. Brown History of Medicine Collection, Buffalo
Wellcome Institute, History of Medicine Division
Yale's Guide to Science, Technology, and Medicine Archives, Special Collections, and Libraries (comprehensive list)

Institutions and Organizations:
American Association for History of Medicine
American Medical Association
American Public Health Association
Centers for Disease Control and Prevention (CDC)
National Institutes of Health
National Science Foundation
World Health Organization