From Kim Jensen:
ColorBlender is a free online tool for color matching and palette design. To get started, choose a preferred color, and a 6-color matching palette (a "blend") will be automatically calculated. Using radio buttons you may switch to Direct Edit mode to tweak or edit individual colors of your blend. Blends can be saved for future use, and will be available whenever you return to the site from the same workstation, given that your browser accepts cookies.