Flutterby™! : Cuboro

Doc linked to Bernie's write-up of Cuboro. When I was a kid, our doctor's office had some marble race track contraptions that had been carved out of solid logs. The Cuboro toys are little wood blocks with holes and grooves cut in them that let you build your tracks on the fly. Pricey, and my personal construction tastes have turned to more raw materials, but they look like fun.