The Noun Project aims to collect universally recognized symbols and make them available in high-res for free.

This project is fairly new (launched early December 2010) and is inspiring for providing for the greater good in the visual world. It helps us to not have to re-invent the wheel. It also helps uncover design/visual history (see author and year created in detailed view).

As the database grows, the ability to browse will be necessary. If something like this was open sourced, it would be fun to synthesize information such as most popular icons vs. most downloaded icons.

Source: The Noun Project