Call me a hypocrite, but while I'm disdainful of Design for the Sake of Design, I'm all for Mechanical Engineering for the Sake of Mechanical Engineering. Dave Johnson's self-built Magnet Machine sends Buckyballs on a little journey with no purpose, but does demonstrate some cool bits of electromagnetic science:
This machine manipulates small spherical rare earth magnets, slicing one at a time from the end of a long chain, moving it around a bit, then dropping it back to re-connect at the tail end of the chain.
It also demonstrates a little snippet of science called eddy currents. Watch how slowly the magnet falls through the aluminum tube compared to falling through air: the falling magnet generates an electrical current in the tube, and that current in turn generates a magnetic field that opposes the movement of the magnet, slowing it down dramatically.