The icons produced by Fam Fam Fam are some of the most respected within the web development community.  Each icon is smooth, with a large variety available for nearly any project.  There is absolutely no cost, although a donation is recommended.

• Price: Free
• Package: 700 16×16 pixel icons in PNG format, totaling more than 1MB in size (ZIP File).
• License: Released under the Creative Commons Attribution 2.5 License, meaning that you may use the set for any purpose, make any changes you’d like, as long as you place a link back to the release page in your credits, or on every page of your website.
• Other: If you want to support the designer, you can donate a little money on the release page.