I ran across this website belonging to an Austrian guy, Paul Schmidinger, and it’s full of neat things, including some incredible Java applets. One of the coolest is Grappa, which comes in six different versions. Basically, you move your mouse around the screen and it draws grid-like lines, influenced by a kind of elastic physics. It’s hard to describe but very cool.
Some of his games are also really interesting, especially Vehicle.
You have got to check them all out.