Adobe Kuler, Color Picker

This has got to be the best color-picker available ( http://kuler.adobe.com/ )on the internet. It is much more flexible than any other i have found, and by far the easiest to use.

Select the color relationships you want and drag the sliders to adjust the colors and tones. The corresponding tones and are adjusted automatically for you. At the bottom of the screen is you can see the values in different color spaces.

For presenters using PowerPoint, the RGB values will be the most useful. Just copy these RBG values into the the PowerPoint color-picker.