Check out the Silverlight implementation of John Conway's game of Life.
Keep an eye on your browser CPU Usage :).
I close everything down, CPU is at 0, I click on the link, the page comes up... I do absolutely nothing (haven't clicked on anything in the SL app, just looking at it) and the CPU goes between 5% and 10%. What's cool about that?!
@Peter,
The cool thing is the game itself. Mark some dots on the screen and press start.
I pointed out the computer usage increase because it jumps up by about 60% for me.