From the folks that brought you the Roomba vaccum, comes "iRobot Create":
I been follwing the Roomba cause on a bunch of the maker and hacker sites, this has been the target of some investigation -- and iRobot thought enough to add a programming port to the Rooba at some point. Now they've removed the vacuum part and just given the maker-hacker community "base robot" that folks can play with. Great idea. Here are some projects:
iRobot Create Projects
Read more at Make Magazine and this review at ROBOT.