Whenever I'm working on a color scheme, I often start with an image or photo to use as a basis. I will then go and suck out some of the colors I like. For the longest time I had been using a freeware tool to grab the color under the cursor, but the blasted tool had a bug which would cause it's window to blank out, and otherwise cease to function correctly.
Having finally reached my limit of patience this weekend, I went and wrote my own version of it:
Basically it shows whatever color is underneath the cursor. Pressing Alt-C will copy the RGB value onto the clipboard allowing you to paste it into your CSS file (or wherever you need the color value).
Color Grab Download (zip 160k), free to use, runs under Windows.