<a href="http://www.sciencenetlinks.com/index.php" target="_blank">Science NetLinks</a>
<span>Science NetLinks' role is to provide a wealth           of standards-aligned resources for K-12 science educators, including lesson plans, interactive lessons and           reviewed Internet resources. Science NetLinks is a dynamic site with new content           being added on a regular basis.
</span><a href="http://www.sciencenetlinks.com/interactives/systems.html" target="_blank">All Systems Go</a> is a good example of what is offered.

<a href="http://www.getbodysmart.com/index.htm" target="_blank">Get Body Smart</a>
This site offers tutorials and quizzes divided into may categories of anatomy and physiology.