Gradient by ShopFactory is a great tool for finding wonderful gradients, to use in your next project. It allows you to manipulate the gradients based on color, pigment and lightness.
Color palettes generator, ColorSpace is a space for everything that has to do with color palettes and gradients.
The super fast color schemes generator! The Coolors app allows you to create, save and share perfect color palettes in seconds!
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.