Our pal Darius Monsef of COLOURlovers blog has created a new web-based color palette tool called COPASO:
COPASO is an advanced color palette tool that helps you create the perfect color schemes and themes. With a scratch pad to save colors you're working with, a photo tool to extract colors and an advanced color picker and color theory wheel to give you all the color inspiration you want. Using COPASO you can save your palettes to a private folder or download them to your local computer.
It's geared for designers and "color enthusiasts" (what does that mean, Darius?), but it's kind of neat to play around with.