Silk is a fantastic set. Been using it for years and haven't found anything more versatile.
Also recently came across the excellent (CC-licensed) Fugue set.
Also recently came across the excellent (CC-licensed) Fugue set.
http://www.tutorial9.net/resources/108-mono-icons-huge-set-o...
and
If I were a more cynical man, I might even suppose that was exactly the reason for producing a royalty-free icon set -- to drum up business.
What better way to show your skills to people who would contract you than to point at something as popular as his icon set?
Not that there's anything wrong with it whatsoever.
I have done almost no icon design since this set was released; The icons have garnered me some personal infamy, and I make a little from text link ads, but I would kill the site if not for the fact that people still appear to find the icons useful and reliable.
For personal work, I use the fugue set linked previously.