If you aren't up for building the bristle bot show in the instructable, you might consider the book Invasion of the Bristlebots (below) which comes with two electric bristlebots.
From the book/kit description:
Invasion of the Bristlebots comes with two mini-robots — basically motorized toothbrush heads. These guys zoom around like caffeinated cockroaches, spinning, skittering, and bouncing off walls. Resistance is futile. The book bristles with ideas for robot games and activities. Race robots against each other. Use the included punch-out walls to construct a Bristlebot maze. Stage a robot sumo-wrestling match. You can even customize your Bots with the provided wire legs, feelers, and beady eyes.
Here's where you can order Invasion of the Bristlebots.