More than 230 sets of over 10,000 high-quality free icons available for download.

Just from a foreign designer's blog, I found a pretty good icon website: www.freeIconsDownload.com. This site offers downloads of over 10,000 high-quality free icons, which is the most comprehensive and highest quality icon collection I've seen so far. Similarly, if you are an icon designer, you can also submit your work to this site.