The National Library of Medicine has spiffed up its online library of more than 70,000 images from the history of medicine. It's a great database to get lost in and the recent upgrade has made it simple to search, download and share the images -- a mix of portraits, photographs, caricatures, paintings of medical scenes, posters and graphic art from as far back as the 15th century.
I could look through them for hours. How else would I come across a wonder such as an engraving of an 18th century toilet designed to look like a stack of books? Or a skeleton with a sense of irony? On a more practical note, the images are largely in the public domain and might well be just what you're looking for to enliven your slide presentation, poster or publication.
Go here for Images from the History of Medicine.
Image above: In this book illustration by Jacques Gamelin (1739-1803), the skeleton appears to be a dab hand at anatomical drawings itself. (Note the sketch at the skeleton's left.)