Google Body Browser, from Google Labs, provides an interactive way to explore the human body. It's been described as "Google Earth" for the human body.
The site is new and you need to use the beta version Google Chrome Browser to use it or enable WebGL support in other browsers.
What's really neat about it, is that you can hide/shade different body systems to explore in more detail. You can move the image around in 3 dimensions, zoom in and out, and get a really good view of anatomy. You can even search for body parts.
This is a good resource for Biology, Anatomy, A&P and medical classes to use.