Adobe Kuler is an online Web 2.0 application that can be used to create colour schemes. These can be based on the rules of colour theory to create Analogous, Monochromatic, Triad, Complementary, Compound, Shade or Custom colour sets using up to 5 colours. Very cool stuff. There's also some nice web links on Kolor Theory.
Adobe has also built Kuler into it's CS4 range of programs, making it easier than ever to design the perfect set of colours. Requires the Flash Player plug-in for your Web Browser.
