If there's one thing a developer should have, it's a good collection of icons. I've got a folder with about 18.7 kajillion icons in it that I've collected over the years. I've tried all sorts of tools to create my own, but lacking any serious form of graphic design ability, I've had to settle for modifying the ones that came with my development environments.

The other day I stumbled across a forum post (I can't remember where, I'll have to look it up) which made reference to a company called GlyFx. These guys have several great libraries of icons for more than reasonable prices. They cover everything from document manipulation through to database stuff. On top of that, they have a couple of free sets that contain heaps of useful standard icons. Go check them out.