Ferrofluid is a lot of fun to play with. You can always buy it for your own experiments or invest in premium displays that let you play with ferrofluid without things getting messy. Take the MTR Designs Rize for instance: it is a beautiful magnetic sculpture with blue ferrofluid and LED light.
To get started, simply put the sculpture on the magnetic base to see the fluid spike and rise up to the top. You get a magnet to interact with it.