A great tool that generates linear gradients, with the ability to customize each gradient, and download the CSS gradient code.
Color palettes generator, ColorSpace is a space for everything that has to do with color palettes and gradients.
Color Hunt is a free and open platform for color inspiration with thousands of trendy hand-picked color palettes.
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.