Being the programmers that we are, design isn't always listed as one of our stronger abilities. Every programmer should have a sense of design, however. Otherwise, every application you would ever use would be far less useful and be much less appealing. Aesthetics are everything.
ColorSchemeDesigner allows any user to create breathtaking Color Schemes for any purpose in it's quick and easy-to-use interface. It allows you to use the color wheel to make precisely correct schemes. Options include: monochrome, complimentary, traids, tetrads, analogical, and accented analogical schemes. All are fully customizable and mathematically correct.The site even allows you take your color scheme and test it out on a test page for web design. You can do anything from sharing the exact scheme to your friends, to downloading it as a Photoshop of Gimp Color Scheme, XML, or plaintext file. It even will allow you to download your ColorScheme as HTML / CSS ! What a time saver!
Other services (like Adobe's Kuler), aren't nearly this functional, and do not offer nearly as many features to its users. The best thing of all is it's free.
Give ColorSchemeDesigner a try!