I wrote recently about some very nice HTML icons which Veerle Pieters created and released for free.
Unfortunately, the icons were in JPG format, which restricted their possible uses (they were also released in MacOS icon type, but this format cannot be used in the Web, obviously).
To my deligh, after a few commenters (including myself;-) asked for a PNG+alpha version, Veerle most happily shared it with us, too! :-)
You can download the icons from her website and/or from here (the distribution of the icons is absolutely free and unlimited, as well as their use):