Feather Icons - Simply beautiful open source icons
The Noun Project - Creating, Sharing and Celebrating the World's Visual Language
IconStore - Free icon packs by first-class designers
Freepik - More than a million free vectors, PSD, photos and free icons. Exclusive freebies and all graphic resources that you need for your projects
IconBros - Free and continuously growing high quality icons
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!