http://www.objectmentor.com/resources/fun/wator/index
Came across this site while researching various TDD methodologies. Its an OO approach to visualize a predator/prey model. You need to watch it for a while to fully grasp the "drama" of the greens vs. the blacks. Its even more interesting if you view the source code to see how its all put together. A great white OO example :)