Nucleo - Commercial vector icons and accompanying apps to manage and customize them.
IconStore - Free icon packs by first-class designers
Endless Icons - A collection of free flat icons and creative stuff
Iconjar - Store all your icons in one place, just a click away
silhoutteAC - More than 47,000 vector silhouettes for free
Streamline icons - The world’s largest icon pack library - 100k icons and illustrations.