12 x 12 px icons (or smaller)
Bullets
Mini web icons 1 (grayscale)
Mini web icons 2
16 x 16 px icons
System icons
Document types
Web services
I'm not really making these anymore. You might be better served by checking out these sets, which I love:
On Amazon at least, a tab per store or category hasn't been possible for a long time. We have the strange break-out menu tab for "See All n Product Categories" instead. When you're browsing within one store, that store label is shown as the selected tab.

Not terrible. But, the tabs have lost their usefulness and the evolution of Amazon's tabs shows how they're a pretty poor metaphor in terms of scalability. Today it's probably nearly impossible for them to discard the tabs given their association with Amazon's brand. The trade off of having chosen tabs from the start is that they're pretty limited in how they can innovate their handling of navigation. There's a lesson to be learned bout navigation design in observing Amazon's evolution.
Strange thing, incidentally, is that on Netscape Navigator 4.x and Safari, the navigation seems to show the old tabs -- their seemingly arbitrary selection of featured stores.
Dan Cederholm shows how to create an icon.
Robert Berdan's excellent article on composing photographic layouts.
Andrew Johnston's design portal.
The psychology of pricing graphic design services.
Martijn van Welie's design patterns collection.
Inspired by Bullet Madness, I updated my mini icons page with the micro icons/bullets I've been using on urlgreyhot and on the spoonsacrossamerica site that I've been working on this past year (not launched yet.).
Unfortunately, the bullets I uploaded to Bullet Madness went wacky and got double posted. Also, for some reason, the transparency was lost in my info bullet. Wierd.
Bullet madness is a growing list of mini bullets, arrows and icons.
The Eyetrack III research released by The Poynter Institute, the Estlow Center for Journalism & New Media, and Eyetools provides some insight into where people looked when they used a set of test web sites.