Noun Project

The Noun Project is building a free online collection of downloadable symbols.  Their mission is to collect, organize and add to the highly recognizable  symbols that form the world's visual language.  You can currently browse the symbols and download any of them for free to be used however you want.  The Noun Project is also a Kickstarter project, looking to raise money to improve their website by adding new features such as Search or Collections.  Every pledge of $30 or more gets a customized t-shirt featuring up to 3 noun symbols of your choice.