I was playing around with Ruby using the Gosu graphics library a few weeks ago whilst waiting for our internet connection to be sorted and ended up kocking together a biomorph implementation in about 200 lines of code (and that was me being verbose, gotta love Ruby).
Biomorphs are virtual creatures as described by Richard Dawkins in his book The Blind Watchmaker. I guess the point is to show how relative complexity can develop from simplicity in surprising ways using a few simple rules.
The Rubymorph script can be found on Github.
Here is a quick example of the sort of thing it can generate:
