Finding a color scheme with matching colors is an art, although there are some guidelines. Most of these guidelines are based on understanding the color wheel.

Kuler is a very nice application that encodes a number of these guidelines and that guides you around the color wheel to at least get some inspiration when it comes to finding matching colors.

Kuler is provided by Adobe, it is free, it is intuitive and it is online. It also features a set of already made sets of colors provided by the community. I highly recommend it. It is worth at least a short visit.