List of Icon Image Resources
Fam Fam Fam (www.famfamfam.com/lab/icons/)
Brand Spanking New (www.brandspankingnew.net/archive/2006/12/hohoho.htm)
Pinvoke (www.pinvoke.com/)
Sweetie (www.sweetie.sublink.ca/)
Random Jabber (www.randomjabber.com)
Free High Quality Icons
At the Wikipedia Commons you can download a fantastic set of icons for free.
The set is called Crystal Clear. Enjoy ;)
For a full listing of the Icon sets available at the Wikipedia Commons website click here.
Also, check out IconFinder, an icon search engine.