Lego Mindstorms NXT is the new version of Lego's Mindstorms robotics toy, featuring simple to use GUI programming, an "intelligent brick" containing electronics to control motors and sensors, and various standard Technic parts. This includes a number of robots included on the CD, more you can download from Lego's website, and of course anything you make up yourself.
As an experiment, I took this robot and attempted to create a program to explore rooms instead of just picking up a ball.
Using the Ultrasonic sensor, it will rotate 360 degrees and attempt to detect the furthest distance. It will then point that way and drive, until the distance is <50cm, at which point it will start again.
Sadly, due to limitations in the ultrasonic sensor (and the fact it keeps dropping to point at the ground), but for those interested I shall provide the project file here.