Scroll down and make a cool Spirograph!
http://www.math.psu.edu/dlittle/java/parametricequations/spirograph/SpiroGraph1.0/index.html

Watch cool a Spirograph being created before your eyes!
http://www.youtube.com/watch?v=GTkPjRdzVEo

Not a Spirograph, I think. But still a cool thing.
http://www.youtube.com/watch?v=k1X7-AUDHBM&feature=related