Color Hunt is a free and open platform for color inspiration with thousands of trendy hand-picked color palettes.
uiGradients is a community contributed collection of beautiful multi-color gradients, free to use on your next UI or design project.
Gradient by ShopFactory is a great tool for finding wonderful gradients, to use in your next project. It allows you to control the gradients based on different settings.
Dribbble Color is a wonderful tool that allows you to display all dribbble shots, based on certain colors.