Dribbble Color is a wonderful tool that allows you to display all dribbble shots, based on a certain color.
A very useful free color wheel and color palette generator for designers and developers. You can also upload an image to get colors from it.
uiGradients is a community contributed collection of beautiful multi-color gradients, free to use on your next UI or design project.
Color palettes generator, ColorSpace is a space for everything that has to do with color palettes and gradients.