Paul Bourke's large and somewhat technical site has a lot of interesting mathematical images. An interactive online Genetic Sculpture Park might be of interest - it requires a 3 meg download plugin I haven't tried yet, though. He also has some interesting links. Click the image to visit the extraordinary interactive Soundtoys site. By far the best use of Shockwave I've seen, the site features its equivalent of interactive java applets by a number of contributors.
Interaction generates algorithmic-influenced image and sound.
Here is a limited online interactive demo of the interesting-looking commercial software Soundbox Potatoland is a very interesting site by Mark Napier. Click the image to visit Mark's Newbold's page with a fascinating Java Stuff page and lots more. Sodaplay is an excellent site with interactive java applets in which you can build and play with things made out of masses, springs and muscles. Coolmath has really excellent java applets including a fine Lissajou Generator. Other nice applets are at the JAVA Gallery of Interactive Geometry ,especially Kali, a realtime tesselation applet.