The Rooma from iRobot has been around since 2002 and has sold millions. However a new model has been produced every year since and they keep getting better and better. There is even a model called the Scooba that will mop and dry the floor for you.

Running on a rechargeable battery, Roomba roams around the entire house vacuuming as it goes. It knows where drop-offs are - so it wont fall down the stairs - and after its hard work is done it will return to its charging doc.