Color Picker
It gives you five ways of viewing and choosing your colors, as you can see in the icons across the top.
The circle is the easiest to use. Click around the circle to choose the color you want. Raise and lower the slider on the right to make it lighter or darker.
You can match any color you see on your screen. Click on the Magnifying Glass to the left of the top color bar, then hold your cursor over the desired color (you don’t need to hold the mouse button down or drag). Click, and the color bar will take on your chosen hue. If you don’t like the exact shade that appeared, click on the magnifying glass again to choose another one.
You can also store your favorite colors for future use. At the bottom center of the Color Picker window is a tiny dot. Click on it and drag down. A grid will appear with hundreds of color blocks. Drag the color bar at the top of the window down over a square, and let go. The color will now be stored to use again in this document, or any other time in any other program!
I agree that the “circle” is easy, but the easiest has got to be the “Crayon” selector. Limited colors, but super easy. (fewer choices-less options to deal with) Print and illustration people will really appreciate the Pantone and swop picker. Web designers will find the “web only” color picker handy.
Also don’t miss Panic’s developer color picker if you work with HTML/CSS/Cocoa etc:
http://www.panic.com/~wade/picker/