If you are a web designer or a programmer with a sense of site aesthetics, visit Pinvoke.com which has a HUGE! collection of icons (as of this writing 2225 icons) in PNG format distributed under Creative Commons Attribution License.
Yusuke Kamiyamane has given a thought in developing this extensive set of icons which will definitely be a handy collection in structuring the sites. Kudos to Yusuke.
