These icons are great for customizing computers and use in design or other projects (though as always, check the copyright and licensing for public usage).
Editor Update: there are now 293,130 icons / 1,487 iconsets at the Icon Archive.
The preview for new iconsets is easy to use and shows a few icons from the set so you don't have to view the whole iconset.
Icons are categorized by topic, from animals to vintage, making it easy to find something specific.
All the icons I had a look at were good quality and available in formats for most operating systems.
Windows users can get a quick overview of how to use icons at these two sites:
XP: Change file and shortcut icons in Windows XP
Vista and Windows 7: Customize Your Icons in Windows 7 and Vista
Icon Archive: Great Icons for Windows, Mac, and Linux
[via What's On My PC]
Off for now,