I was playing with a newly discovered website collection of applets tonight and I found this cute one on “surfing” curves for derivatives. You’ll need an updated Java plug-in for this one.
If you really object to the little guy on the surfboard, you may toggle him off!
The entire collection of Manipula Math with Java applets can be found here. Some of the applets have been done in a more sophisticated fashion by other sites, but it might be worth a browse!