There is a toy for cats, called turbo track. There are alot of youtube videos demonstrating it. Just click here - http://www.youtube.com/results?search_query=turbo+track and watch.
I realized, I can make one with my PrintrBot and OpenSCAD.
It's parametric - you can easili modify and extend it. And adopt to your prefer ball diameter.
Just download provided .stl and extrude.
Or download provided .scad and modify.
Or you can modify source .scad file and send me patches.
Or fork and push patches via push request.
Or something else.
Or more and more.
And even more.