on the BBC...

The BBC in the UK have got some excellent resources on their site.

In The Human Body section there are various interactive activities about the organs, muscles, skeleton, nervous system and puberty. I highly recommend the senses challenge.

Another section, which probably couldn't be used so much as a resource, but for your own intrest is Brain Sex. Although the name sounds a bit rude, it isn't. It actually takes you through a sequence of tests to determine feminimity and masculinity. I found it rather interesting!