Here are a couple of links for sites related to introductory biology:
1) The Online Biology Book: This “book”, hosted by the Estrella Mountain Community College in Avondale, Arizona, contains 58 chapters on topics covered in most introductory biology courses and is a great reference!!
2) “Froguts!” Try your hand at dissecting a virtual frog! This company sells “virtual dissection” software for use in the classroom. Their website has demos of a few of the modules: dissect and owl pellet and reconstruct a rodent's skeleton, identify the parts of a squid, or dissect a frog.
[Note: I found these both of these links on the Discover Magazine Web Picks site].