Easyicon - Search 500,000+ free icons, (PNG,ICO,ICNS) desktop icons, icons Download.
This site has loads of icons from various authors covered under different licenses. They are all generally free to use but for personal use. There are some for commercial use but i can not tell you in what ratio. Each icon clearly display the usage terms. I find the search is easy to use so the site is hassle free.
The only downside is you cannot filter the search by license type, i have sent a suggestion to the website owners and also suggested a clear explanation of the licensing terms as this is lacking and can be confusing.