I found a pretty neat tool at Vision Australia, Colour Contrast Analyser 2.2. Although it may be used as a color picker it's main function is for finding color contrast combinations that work well together with text. While useful for web design this is very important in any graphic design using text. The Color pallet has an interesting feature showing 10 shades of the currently selected base color in varying degrees of opacity. A bonus feature analyzes color combinations related to color blindness. It's small, free and portable. Windows only I believe. Be sure to read the instructions page.

Colour Contrast Analyser 2.2