Flaticon - A database of free vector icons.
Icons DB - Search through more than 3300 free icons. IconsDB let's you customize and download icons.
IconArchive - Search through more than 735,000 free icons. Browse icons by category, artist, popularity, date. Organize and share your favorites.
Icons8 - Free app for Mac & Windows already containing 39,800 icons. Allows to search and import icons…
Game-Icons - Huge collection of free icons for games and apps.
The Noun Project - Creating, Sharing and Celebrating the World's Visual Language