Plasma Pong!

http://www.plasmapong.com/

It requires a download, but it's awesome! The music is cool, too, until it gets so fast it sounds like the game's going to blow up.
Just try it out for yourself, it's pretty cool.

Warning: you do need a half-decent graphics card and processor to run this well, as said on the site. 32 MB integrated cards work (I have one on my laptop and I get about 12-15 FPS, which is plenty enough), but I doubt an ATI Rage will suffice.

 

wow what will they come out with next....