Krafty Librarian has done a great job of compiling a complete list of the medical podcasts in a downloadable MS Word file:
"I have sifted through a lot of web sites, lists, and iTunes programs.
Please feel free to suggest any that I am missing.
As this list grows it may be necessary to create two lists: those for consumers and those for medical professionals."
UBC Google Scholar Blog features the Top Five Podcasting Articles in Medicine (March 2006).
Krafty Librarian has updated the list of medical podcasts:
"When I first started on this endeavor I found eight podcasts, five months later the list grew to 34 podcasts, seven weeks later I have a list of 52 podcasts."
Update 06/16/2007: More links
Podcasts and Videocasts. UBC Health Library Wiki.
Podcasts and vodcasts in medicine. Dean Giustini (PDF)