I recently stumbled across this free icons website that has a large collection of high quality icons for download. The quality really amazed me and there are over 15 different categories to choose from. As usual make sure to take note of any usage terms before you get excited and start downloading a bunch of free icons!
They also have a most downloaded page which will give you a quick glance at which icons are being used the most. If you have some icon design talent, you can submit your icons to the site and be rewarded with backlinks and traffic!