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!
Feather Icons - Simply beautiful open source icons
1000 Detailed Creative Icons - Carefully designed icons with tons of fine details
Animated Icons from Icons8 - Massive collection of full-motion animated icons to make your project shine
Icons Mind - The Biggest iOS 8, iOS 7 & Android Icons Pack
IconStore - Free icon packs by first-class designers