I picked up on an awesome Color Contrast Checker from Jonathan Snook, and wanted to check and see how my stylesheet held up. Rather than digging out all the colors I was using, I re-developed his Contrast Checker to make it a Web Color Contrast Checker which can run against a set of colors at once. It will even parse your stylesheet for you.
Of the major updates beyond handling multiple colors at the same time, and loading colors from a stylesheet; you can specify colors in either #ffffff, #fff or rgb(255,255,255) format. Don't forget to check out the original specification for color contrast compliance.
When you find your colors stink, head on over to the Color Scheme Generator to get your fix.
Again thanks to Jonathan Snook for his version, and 436bereastreet where I originally picked up on it.