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!
Flaticon - A database of free vector icons.
1000 Detailed Creative Icons - Carefully designed icons with tons of fine details
Icons Mind - The Biggest iOS 8, iOS 7 & Android Icons Pack
IconArchive - Search through more than 735,000 free icons. Browse icons by category, artist, popularity, date. Organize and share your favorites.
IconStore - Free icon packs by first-class designers