Better quality: http://www.youtube.com/watch?v=eA1jSlx9c30 (I can't embed this version)
It turns out that it is possible to mix up a non-newtonian fluid very easily at home using only corn flour and water in a ratio of about 2:1. Non-newtonian fluids are really weird substances - under pressure they act as solids. You can grab what feels like a lump in the liquid and have it flow out of your fingers as soon as you stop applying pressure. You can also tap the surface of the liquid without getting wet but if you press gently your finger sinks into the liquid. The most interesting effect is that if you vibrate a non-newtonian liquid the pressure waves cause the fluid to form really cool structures. I don't have a great speaker for doing this but I still managed to do the following.
Here are some better videos from people with much more suitable speakers.