Quackwatch: Guide to Health Fraud, Quackery, and Intelligent Decisions

Federation of State Medical Boards. www.fsmb.org or www.docinfo.org "Your most accurate and trusted source for physician disciplinary information" (fee for each search)

Administrators in Medicine:  "DocFinders." National Organization for State Medical & Osteopathic Board Executive Directors. 

HHS Office of the Inspector General: List of excluded individuals and entities