The Visible Body is a fantastic, free, program that allows your students to virtually explore all systems of the human body. I first learned about the Visible Body through Kevin Jarrett's blog, he used the program with a 4th grade class, but the Visible Body could just as well be used in a high school setting. In fact, the reason that I thought about the Visible Body today is that a science teacher in my school mentioned that she has used it with her anatomy students.
To use the Visible Body you need to install the Unity Web Player for Mac or PC. Once installed you can explore all of the systems of the body. The Visible Body allows students to view bones, muscles, and organs from various perspectives and see how the parts of the body work together as a system.
Applications for Education
As I mentioned above, the Visible Body can be used my students in elementary school through high school. The Visible Body could be used by students individually or as a group activity. The imagery and explanations found on the Visible Body are far better than those found in most public school textbooks.
Update: Kevin Jarrett reminds us in the comments that if you're going to use Visible Body with younger students be aware that Visible Body is 100% anatomically correct. In that case it's probably best to use Visible Body as a teacher-directed exercise and not a individualized activity.