silhoutteAC - More than 47,000 vector silhouettes for free
Nucleo - Commercial vector icons and accompanying apps to manage and customize them.
IconBros - Free and continuously growing high quality icons
Endless Icons - A collection of free flat icons and creative stuff
MakeAppIcon - MakeAppIcon resizes and optimizes your icon designs into all formats needed for iOS and Android mobile app!
Streamline icons - The world’s largest icon pack library - 100k icons and illustrations.