Nucleo - Commercial vector icons and accompanying apps to manage and customize them.
Zwicon - A simple, carefully designed collection of icons
Endless Icons - A collection of free flat icons and creative stuff
Streamline icons - The world’s largest icon pack library - 100k icons and illustrations.
silhoutteAC - More than 47,000 vector silhouettes for free
Vivid JS - A highly customizable, open source SVG icons library