So often there are questions on Medlib as well as other email groups asking for good medical images sites. I have found that The University of Texas Health Science Center at San Antonio (UTHSCSA) Library has a really nice web page listing sites where one can find a great many medical images.
http://www.library.uthscsa.edu/internet/ImageDatabases.cfm#content

The majority of the sites they listed allow the use of the images for noncommercial or personal, however they encourage users to check copyright statements for each listed site.