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!
Nucleo - Commercial vector icons and accompanying apps to manage and customize them.
The Noun Project - Creating, Sharing and Celebrating the World's Visual Language
IcoMoon - IcoMoon is an icon management tool that is build to provide iconography.
Fonts4Free - Archive of freely downloadable fonts for Windows and Mac OS.
Streamline icons - The world’s largest icon pack library - 100k icons and illustrations.