Icon Search Engines

1. Noun project
2. Icon Finder
3. Icon Monstr
4. Icon Seeker
5. Very Icon

Icon Resources

1. Famfamfam icons
2. Icon Archive
3. 2500+ commercially free to use icons
4. Icon Pot– they mention they only list icons which can be used for free on personal and commercial projects without having to provide back-links/credit to the author
5. Icons at Web Apper