This entry is a little off the beaten path as I do not plan on posting many items for web designers or technical pros, but this one, Kuler, is so useful that I simply could not resist.  There are tons of color pallete generators on the web, but none so well done as this one from Adobe, the Photoshop people; go figure.  This is useful for anyone doing design work for print or for the web, even for artwork or presentations. 

An honorable mention in this category goes to color.org.  It is a little bit harder to use,  but you can upload a picture and a color scheme will be generated from the picture.  Very useful if you already have a graphic element or photo from an existing design that will be part of a final product.  Both of these tools are free to use...and if every designer used them we would live in a more beautiful world.