I thought I would share this with the STC as I found it to be a useful resource.

I recently came across the Noun Project. It is a free public domain library of symbols and icons (covering a really eccentic range of topics)

http://thenounproject.com/

I also wrote a bit about it here and linked to an interview with the project’s creator

http://joshstubbs.com/2012/03/11/a-hazard-symbol-is-worth-a-thousand-words/

Josh