Add to this post a video about how to make oobleck, hell if you haven't made it make it your self. Its super neat.

http://www.instructables.com/id/Oobleck/

Its a non-Newtonian fluid, if you punch it or move fast against it, its hard, but if you move slowly with it it will flow like a liquid. Pretty badass, and something really neat for kids as well!

Heck I made it with some undergraduate students before and most had not done it before and thought it was neat as well.