WebGradients is a free collection of 180 linear gradients that you can use as content backdrops in any part of your website.
Beautiful Color Palettes
Color Claim was created in 2012 by Tobias van Schneider with the goal to collect & combine unique colors for my future projects.
The daily color digest
Best Flat Colors For UI Design
Khroma is the fastest way to discover, search, and save color combos you'll want to use.