I really LOVE the I-Sobot. This is one of the smallest robots that can still do really cool stuff, like box other robots, or play robot soccer, or even help you out with your gaming system (that takes a little bit more programming).
This miniature robot can even be programmed with voice commands so you can speak to it, and have it do things. You can also program a series of moves, so you can even have it dance for you.
There are so many things you can do with the I-Sobot that you have to check it out yourself to get the full effect. In the meantime, check out the video showing some of the things the I-Sobot can do.