I have taken a iRobot Roomba vacuum cleaner apart and made an Arduino Powered robot out of it. There is a serial port on the Roomba, but mine was dead so I wanted to do a complete rebuild. I am using a L298 motor controller IC. The Arduino is on the back right corner in the picture below.
At first I was just interested in how much power the Roomba has. It easily got around with about 20 pounds of added weight and could push chairs out of its way. My long term goal is to make a life sized robo-raptor and this would make a nice foot. I have videos of a 2 foot long robo-raptor also under control of an Arduino.
Here are the videos: