Recently, I've started using a new set of icons which, surprisingly, I haven't made myself. They're from the Tango project, which I only found about a month ago.
Although they're aimed at desktop applications, and desktops themselves (i.e. KDE and GNOME), I find that most of the icons are ideally suited to web applications, and web design in general, and can really enhance a page if used correctly. As such, I have been using them extensively in my latest project: my practice AS-level computing coursework, and have found them ideal.
I would encourage people to do as much as they can to help the Tango project, as the work they're doing is good, and the icons they're creating are superb, and free.
On another note, merry Christmas to all those interested.