Simple Robot Ideas?

i just got a soldering gun, and i really want to use it. but my knolegde of electronics is limited (and so is my wallet), so does anybody have a cheapish, simple, and cool robot idea?

To suit your needs, try a bristle bot, it isnt anything special, but you can impress people for this thing moves on its own. It isnt a real robot but not a lot of people know the difference. The only non household component is a DC motor.