Today we'll swing back toward the original reason I started making these-- for maps. I've long had a vision in my head of a dungeon map that conveys most of the information the DM needs visually, no words to read during play. But it has taken me years to try and cobble together the tools to do it. Still haven't found everything I want. But the following might be useful. First, the things I tend to drop around my maps most, are what I consider toys, the magic items that let's players do new stuff:
I'd add scrolls, but I haven't found a good way to represent them in silhouette yet. The idea is to place them on the map and then remember at a glance "oh, this is the room with the ring . . ." I usually can improv interesting details from there. If there is more than one, which there often is for my potion caches, I'll use a number by the map image. That comes from ZakS's idea to track keys that way, or was it scrolls? Either way, it works.
Speaking of keys, here is a lock and key:
The rest are possible dungeon features:
barrels for the Diablo fans:
and a cauldron:
Others I have in mind are trap, ladder, fountain, and arch. Suggest others if you have them. Eventually I plan to put up a dungeon for you all, that is solely visual and see how it translates.
These are all in the public domain, use them as you wish. I've put them in the "misc" folder of my vector graphics zip file linked in my sidebar to the right.