Color Blender - Pick a color value format, input two color values, and pick the number of midpoints you'd like to see. The palette will show the colors you input as well as the requested number of midpoint colors, and the values of those colors.
Try the Color Blender

Easy RGB Color Harmonies - Start with a favorite color (the RGB format in either 0-255 values or hex values) and this great tool will show you color complements and harmonies. Create your own color palettes with this great tool! www.easyrgb.com/harmonies.php

Color Match 5K - This utility will help you select a matching 6-color palette for your website. Define a single color that you like. Matching colors will be calculated. www.colormatch.dk/

Spin the Color Wheel - Try your luck generating random 3-color palettes on a choice of 2 example pages and use the hold button to save a color you like. It's fun! www.colorsontheweb.com/spinwheel.asp

Color Toy 2.0 - An online Flash color schemer. Start with a RGB or hex value, or try their random color scheme generator. www.defencemechanism.com/color/

SlayerOffice Color Palette Creator - An online tool that will will create 10 shades of a base color. You can randomize the base color, view a history of colors you've sampled and much more. slayeroffice.com/tools/color_palette/

Color Wheel Pro - This program enables you to create color schemes and preview them on real examples. Create your own or choose from pre-made color schemes created by a professional graphic designer and then export your scheme in several formats. 30 day free trial available.
www.color-wheel-pro.com

Web Color Visualizer - Set a background color with this online tool and then roll over other swatches to visually see the combinations. www.ideo.com/visualizer.html

Daily Color Scheme - Even though this site is still in beta and doesn't appear to actually be updated daily, there are still some nice color palettes in the archives to choose from. Worth a look! beta.dailycolorscheme.com

Color Palette Generator - Use this handy online tool to customize colors based on a photograph. Simply paste the URL of any image on the web and obtain a 5-color palette in either dull or vibrant shades. www.degraeve.com/color-palette