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!
Zwicon - A simple, carefully designed collection of icons
Flaticon - A database of free vector icons.
Eva Icons - 480 Open Source icons for common actions & items
Fontello - Tool to build custom fonts with icons.
Material Design Icons - 750 Free open-source glyphs by Google