Iconfinder is the best icon search engine. There are a lot of high-quality icons available, and you can filter the results to show only those that are licensed for commercial use.
Icon Fever is our own gallery site of icons. You can browse icons by license to find those that can be used for commercial projects, and you can also browse by tag.
Icon Seeker is a useful icon search engine. You can also browse the popular icons or use a tag cloud to find what you’re looking for.
IconArchive includes almost 30,000 icons that can be searched or browsed by category. Licensing information is available for each icon.
Free Icons Web includes over 18,000 icons that can be searched or browsed. Icons included here are free for personal use.
Very Icon is a search engine that includes an advanced search option and categories that can be browsed. Over 20,000 icons are indexed.
365icon is a gallery site that showcases excellent icons. The archives can be browsed by style/category.
Icon Easy is a gallery-type site that includes a large number of icons. They can be browsed chronologically or by category.
IconDB is a search engine that includes a wide variety of icons that can be downloaded.
Iconza is different from any of the other sites listed here. It provides a set of free icons that can be customized to match the colors of your website.
Here’s some other articles that you will definitely find useful.