The Color Scheme Designer by Petr Stanicek is a site that lets you play around with colors. Choose monochromatic, complement, triad or other options, and it will suggest a color scheme for websites etc.. You can easily choose which colors to use and even see an example of a website layout with your chosen colors. You can also see what it would look like to a colorblind person. Once you’re happy with your colors, you can export the color codes for html, for example.