some of my favorites: [wellstyled.com...] gives suggestions according to 4 different schemes - mono (lighter/darker of same color), contrast, triad, tetrad, analogic [validhtml.com...] in German, but you don't have to know German to use it - simpler, only one set of suggested colors corresponding to the base color you pick, but very easy to use and the colors it produces are interesting, but very nice harmonic combos
