Link: Open Icon Library - Free/Open IconsQuote:
A free and open Icon collection. Over 5000 Unique Icons. Free for anyone to use on you computer, website or any other project. The library is not a theme. Its a centralized source for icons to cover all your needs. The goal is to cover all common apps, operating systems, mimetypes, devices, and country flags.
I downloaded the Windows desktop icon archive [5,375 icons in the 48 x 48 folder] I found that Windows had problems dealing with the ZIP archive [opened it eventually but it took a while] so I used 7Zip instead.