Dmitry Baranovskiy, author of the Raphaël JS Javacript vector graphics library, has released a set of icons designed using the library:
"130 Icons " - http://raphaeljs.com/icons/
Remember as these icons are rendered using Raphaël JS they are vector graphics (in Firefox they with render as SVG, in Internet Explorer as VML), not bitmap graphics like jpg and png, so they will look crisp at any resolution.
Updated 2021 : note that the above post was originally published in 2010, but is left here for archival purposes. It seems the link to the 130 icons no longer works, so I have unlinked it.