There are thousands of free icon collections out there. Most of them are oldies or full of spam and popups.
Today, I´ve discovered the best free icons web site Ive seen.
http://www.iconarchive.com
Mostly because:
* It has thousands of icons
* They are categorized
* The download links aren´t one thousands clicks away
* Most icons are pretty new, with an excellent quality and HiRes
Be careful with the copyright of some of them if you are going to use them in your projects.
Enjoy!