Here is a really cool, “free for now” app from Adobe called kuler.
“kuler is the first web-hosted application from Adobe Labs designed both to stand alone and to complement Adobe® Creative Suite® 2 components. Built using Macromedia® Flash® and ActionScript 3.0, kuler is all about color: color for exploration, inspiration, experimentation and sharing.” You need to have the latest version of Flash installed on your computer, and that’s about it.
Read more about kuler at Adobe Edge, Adobe’s online magazine.
It’s fun! Go to Create, where there’s a color wheel with little sticks that you grab with your mouse to choose a color. You can create your own color harmony, or choose one of the standard color harmonies (analogous, complementary, monochromatic, etc.). Below the color wheel are 5 squares of color, each with three sliders to regulate the hue. And below the sliders, are the RGB, CMYK, HSV, LAB, and HEX codes for those of you that do graphic design/web design.