Hi,
I have altered my artificial life simulator Critterding to make use of Bullet Physics. I think it will make a good foundation for adding more complexity to it.
Homepage:
http://critterding.sourceforge.net/
Here's a youtube vid I made a while back:
http://www.youtube.com/watch?v=eaG-ttwCTNE
and one done by someone else:
http://www.youtube.com/watch?v=JsWfeXGWhxg