Every year, www.the5k.org runs a coding contest for DHTML & Flash sites/pages which total <5KB in size!!!
As ever, there are some brilliant entries this year - check out the winners here:
(If you have a lot of time on your hands, you might want to check out some of the other entries that didn't make the various top 10s, as well as the winners from previous years!)
PS - I'm still going through them, but Window Pong is my current fave!
Now it's Wolfenstein 5K
....! Dig that JS raycasting + texture-mapping engine!