Iron filings move to the music above an array of computer-controlled magnets in TechnoFrolics' "Choreographed Iron Dust" display shown at last weekend's World Maker Faire in NYC.
Ferrofluids are basically just iron nanoparticles suspended in a liquid. In the presence of magnets, they do some pretty cool things. For instance, ferrofluids flow to place where the magnetic flux--the strength of the magnetism--is strongest. So if you magnetize the screw from a meat grinder so the magnetic flux is denser at the top than it is at the bottom, the ferrofluid will climb the screw like staircase.