Although you may be able to match your own clothes in the morning, finding just the precise complementary colors is sometimes a pretty daunting task, or at least a time-consuming one. How do you pick out four colors that work with your client's logo?
ColorTheory from Digital Anarchy provides a pretty quick answer. The interface is clean and simple, but generates powerful results in a variety of color schemes. The Pro version adds the ability to load a source graphic in to compare with your colors. It also adds the ability to run ColorTheory as a plug-in from Photoshop or After Effects-compliant hosts.
The product is priced at $49 for the Standard version and $99 for the Pro.