Other honorable mentions

Ndesign provides 320 icons for your use. Download here.

BrandSpankingNew offered as a Christmas present last year a wonderful set of 113 grayscale (albeit rather small-sized) icons that you can easily use. Download them here
Brand Spanking New

To easily identify the icon you want, switch to "Thumbnail view" in your explorer.

Free icons Free icon sets for your website

After noting famfam.com went down some time ago while looking for the great icon set I have decided to help out by providing the entire 1000-icon Silk set here. Click on the thumbnail below to see the entire set.

Preview click for more

Download Silk 1.3 here

A nice variant on the famfam set is provided to us by pinvoke with the PI Diagona Pack.

PI Diagona icon set

Download the PI Diagona Pack here.

For the serious Photoshop folk, Crystal Clear is a fantastic collection of icons that you won't find elsewhere (I used the headphone icon for a recent project and am very satisfied with the result.)

Crystal Clear icon set

Take a peek at Crystal Clear here.

Tango! is another great resource (albeit an odd one, since it's for desktop environments) that allows you to give a sort of Ubuntu/Linux feel to your website.

Preview click for more

You'll want to cut and snip the icons you want with your favorite graphics editor. Visit the Tango! website here