Some color experiments using the iPhone app called Peppermint. I do these when I'm stuck waiting in line somewhere or when I take a little break. It's a good way to take a quick break from drawing and avoid wasting time on Facebook or Twitter. I've included a screen grab of the Peppermint app so you can see one of the color wheel tools.
Anytime I need a new color palette for an illustration or design, I pull these up to help speed up the process. Adobe's Kuler works in a similar way and ties into all the Adobe apps, but I do find the Peppermint iPhone app a bit more convenient since I can play with it just about anywhere and quickly crank out a few color experiments.