My review of David Macaulay's new book The Way We Work is up at GeekDad. Although ostensibly for younger kids, at 363 pages it's definitely suitable for middle and high school students. Macaulay spent 6 years laboring on this book, four of them just learning anatomy through means that included attending operations and dissecting corpses. You can find out more about Macaulay's techniques at his website.
For lower grades I heartily recommend the book mentioned a few posts back, The Human Body Book and See-Through Model by Luann Colombo. While the "visible man" was rather chintzy, it was helpful to put the organs together while learning about the related system ... plus it wasn't too gross looking sitting out on a shelf.
Another book we liked a lot when they were little was
From Head to Toe: The Amazing Human Body and How It Works by Barbara Seuling. The illustrations by Edward Miller are much more stylized than anatomically correct (so to speak), but probably just enough for really young kids. The book includes several projects, including the robot hand (example here) I later borrowed for a Home Education Magazine column. If you go to Miller's website and click on "Activities for Kids" you'll find an additional project that lets you print out and paste the organs on a drawing of the human body. My boys enjoyed doing that one as well when they were small.