I learned about this site from @Ktenkely on her website iLearntechnology. It's an interacitve site that allows you to create Jackson Pollock style paintings without any of the mess. This is great fun on the Smartboard. By clicking the mouse you change to a random color and splashes of paint appear as you move the mouse across the screen. JacksonPollock.org is a wonderful site that art teachers can use that will save you a big cleanup in the future.
I let my students play with the site on the IWB and they loved it. They loved the randomness of the colors and how there was no "wrong" way to create the painting. I recommend using this in any class where you might have some time to allow your students to explore their creative side without needing a smock. :-)