You know those paint color sample strips that you typically see in home improvement stores? They usually have different shades of the same color on individual strips so that you can easily compare and fine-tune your color choices. Shades 1.0 applies this same methodology of color selection to the standard Apple Color Picker within OS X. With this little utility installed, any application that uses the Apple Color Picker will be transformed to display a color grid once you select a center color, step size, and a constant color coordinate (of H, S, or B). And with this handy grid, you can tweak your color choice even further for precise customization. Ok, so this utility probably best serves only the truly obsessive among us, but the concept is still pretty nifty, I think.
Shades is shareware, and will set you back $14.95 for a full license.