Font Awesome - Font Awesome makes it easy to add vector icons and social logos to your website. And version 5 is redesigned and built from the ground up!
IconStore - Free icon packs by first-class designers
1000 Detailed Creative Icons - Carefully designed icons with tons of fine details
Feather Icons - Simply beautiful open source icons
Icons Mind - The Biggest iOS 8, iOS 7 & Android Icons Pack
Noun Project for Mac - Search nearly a million icons. Now in color!