I was wandering through Smoking Apples earlier today, and ran across their article: Deconstructing the Mac OS X Color Picker. Now, honestly, I do not use it very often.. but it is a very useful tool to keep track of a few favorite colors, and an easy way to pickup new colors from something else on your screen.
They also mention a few plugins, one of which I am going to grab ASAP: a hexadecimal color picker, which you can use to get color values for use in your web pages.
Last, and not least, is the super simple way to open the picker from anywhere! Make a new script in your Script Editor and type in ‘choose color’ and save the script as an application. When you run it up comes the color picker! Feeling too lazy to open Script Editor? The folks at Smoking Apples made the script and put a nice icon on it already. It’s in their article.