Mark Tilden explains doing a whole lot with just a little with a BEAM robot from 1995 made a Walkman motor. ;-) See the video below.
Solarbotics (see sidebar) is still "the" source for all things BEAM and lots of other fun stuff too. One of the ideas of BEAM robotics is doing a lot with a little - engineering at its heart!
Thanks to wikipedia for all the good info!