IconStore - Free icon packs by first-class designers
Flaticon - A database of free vector icons.
Noun Project for Mac - Search nearly a million icons. Now in color!
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
IconArchive - Search through more than 735,000 free icons. Browse icons by category, artist, popularity, date. Organize and share your favorites.