When you're designing a website, you're often in the need of icons to make the navigation more intuitive. But when you're not a company, you won't often have the money to buy a license of a big professional icon/symbol pack. Hopefully, some very nice work is available in permissive licenses, like CreativeCommons.
FamFamFam is one site that propose such work, that you can use according to the license terms (see the reference at the bottom). About 700 PNG icons are available in 16x16 format, and other collections propose GIF and PNG sets.
Related sites: