A free library of downloadable symbols
(you might have to use Firefox to access the site.)
"The Noun Project was born one year ago. We launched the collection as a free library of downloadable symbols made mostly of the National Park Services, AIGA, and Universal Health Care public domain symbols. Today, that library has expanded to include more than 800 symbols created by our designers, collaborators, and - most excitingly - by users from around the world. It is no longer just a library. It's also a workshop, where concepts are visualized and shared freely. It's a new way of thinking where language is seen, not spoken."
The design process in action (video)
Short video made with icons