Alchemy web site and virtual library - by far the largest collection of alchemy on the web. 

Ancient Medicine - Medicina Antiqua

The Asclepion - a web page devoted to the study of ancient medicine from Indiana University.

Aspects in Ancient Medicine - University of Virginia Health System

Chemical Heritage Magazine - published by the Chemical Heritage Foundation

Founders of Science.net

History of Medicine Collections - Duke University

History of Medicine Division - National Library of Medicine

History of Medicine Links, University at Buffalo

International Bibliographic Guide to the History of Pathology (IBGHP) - from Heidelberg, Germany

Karolinska Institutet (Stockholm, Sweden) History of Biomedicine

MedWebPlus: History of Medicine

Museum of the History of Science, University of Oxford

Needles in Medical History - The Wellcome Trust

Sciencemag.org History/Philosophy of Science

Selected Internet Resources in Biomedicine - Yale Cushing/Whitney Medical Library

The History Channel - Search for quick topics

The Truman G. Blocker, Jr. History of Medicine Collections  

University of Michigan Historical Center for the Health Sciences - Internet links to numerous history resources. 

The Wellcome Trust - History of Medicine

WWW Virtual Library - History of Science, Technology & Medicine from the Australian Science Archives Project