No-one can even have too many icons to use on websites.  So now, to go with your famfamfam and Fat cow icons, we have Fugue, a set of 2,757 icons (and frequently updated it seems).  You can also get the PSD’s for everything in this set as well.  The style is different to the others, but these are still available at 16×16 so perfect for navigation icons, admin area etc.

The icons are free to use, providing you have a link back to the designers site, otherwise you can purchase a royalty-free licence for $59.95 USD, which at the time of writing is £38.99 GBP.

There is a much smaller set of 400 icons also available for $9.95 USD.  Do check the licence on the site which at the time of writing, for both sets of icons, is Creative Commons Attribution 3.0 license.