Check out my project I made for Solarbotics. It is a rolling robot inside a plastic ball.
httpvhd://www.youtube.com/watch?v=IwIRV_WmQ7A
If you want to build your own wanna be miniball, please visit :
http://www.instructables.com/id/Solar-Powered-Miniball-Wannabe/
This is the first time trying to embed a instructables!