The web has many digital tools for creating color schemes that are based on traditional analog design interfaces: color wheels, bars, and sliders. Probably the best-known of these is Kuler, but there are some good alternatives:
Color Scheme Designer is a tool that not only allows you to create arrays of hues using the techniques I’ve explored in a previous article, but it also allows you to simulate the same hues under conditions of color-blindness, see them used in a mock layout, and export them as HTML + CSS, a PhotoShop palette, or as a URL you can share with others.
0 to 255 is a great way to generate close variations on a hue, or monotone color theme. (Uses Flash).