IconCool collects Icons for Windows XP. There are 16 icon sets, which can be downloaded for free. Most of them include original icons from Microsoft. Links checked: June/04 2008 – 3 sets deleted.
14 sets in .PSD-format for image editing in Photoshop. Themes are Documents, E-Mail, User, Weather, Folders, CDs, Books, Bullets and further toolbar-icons.
The Gallery 2 Web Icon Set, created by Paul Armstrong, includes 75 Mini-Icons. It is licensed under the GNU General Public License (GPL).
Web Control Icons Set doesn’t offer exceptional icons, however they might be just what you’are looking for developing a simple and user-friendly web-application. Public Domain icons are available in three sizes:
Grey, but professional and serious – 40 Icons provided by e-lusion.
Toolbar Icons by Matt Ball
Mini-Icons, is it possible to create smaller icons?
Icon Editors and Button Generators: