I just got a Sony Ericsson CAR 100 Bluetooth remote control car. It charges from my phone (a T616) and can be controlled with the phone’s joystick. There’s also a Car-100 control application for the Mac, which lets me control it with the arrow keys.
Cody & Midnight find it very amusing. I’ve been driving it around them and they love stalking it. When I make it stop, one of them will come over and start pawing at it.