Something that caught my eye on a link off a link off Slashdot* and which seemed pretty damn cool was some guys experimenting with ferrofluids. You can get some really cool patterns when you apply a strong magnet to a bunch of small ferrous particles suspended in a fluid.
* Slashdot and wikipedia link jumping has become one of my main and favorite pastimes online. It’s surprising what cool stuff these two sites link to (whether it’s interesting articles on wikipedia, which contain links to other interesting articles ad infinitum, or reference links within Slashdot posts, which themselves contain interesting stuff, or contain links to other interesting stuff)