You can chose between mono, complement, triad, tetrad, analogic and accented analogic color combination. After Colorschemedesigner gives you scheme you can adjust it.
Adjustment is available for saturation/brightness and contrast. You can do that manually or chose from drop-down menu (more, less, min, max contrast, dark saturated, pastel, dark pastel, pale dark pastel, almost grays, almost grays with color accents, and few more varieties).
You will get color codes, and you can export scheme as HTML+CSS, XML, Text, ACO (Photoshop palette) or GPL (GIMP palette).
In real time, you have scheme preview. You can also get preview of scheme in dark or light website template to see color scheme you make in real action.
Visit Colorschemedesigner: http://colorschemedesigner.com/