Ever need to find out what a color on your screen is in hex or rgb? Anyone doing any kind of design work has probably run into this before, and there are things out there you can install to do this... But I just discovered that OS X has a tool for this built in, and it's really quite good!
It's called DigitalColor Meter and is located in Applications/Utilities. Usage is pretty straight forward, you pick from the drop down how you want the colors (RGB, Hex, etc) and then when you point the mouse at the color you want press cmd+shift+c to copy the color to your clipboard.
Another interesting color tweak you can do, is add Adobe's Kuler to your OS X Color picker (used in all apps) via this interesting plugin.