At the moment, my players' characters are in a city on an island. So they are neither at the mercy of the random wilderness encounter tables nor of a stocked dungeon. I'll be improvising a lot and I want my toys where I can get to them, but I don't want to have to make up a brand new encounter table for every single environment every single day.
So here's what I've done--
First, I made a folder on my computer with one picture for every single monster I like. I just used whatever picture I could find--some I'd already drawn, some I googled up. I didn't worry about whether they were good, just whether I could tell at a glance what the monster was. (Click to enlarge.)Then I made a picture of a big white field with some labels for basic categories of monsters--sorted by behavior. Here's that picture:
Brutes are like big dumb ones--usually animal-intelligence-level predators, Soldiers are mostly intelligent humanoids, Automatics are guardian-types or other automatons that "activate", Vermin are little things that just want to eat and mostly get in your way, Schemers are villain-types, Summoned covers anything that will usually show up just as the result of somebody casting a spell and Weird are creatures which have some other niche and require a little thought to get into an adventure.
Anyway, then I go over to "system preferences" and make the picture with the labels into the background for my desktop...
Then I slide all the stuff on my desktop to the side (those of you groaning at the idea of cleaningup your desktop--I know how you feel. I just threw everything into a folder called "not now, love" which I'll pull open when I'm done with this.)
Last, I go to the monster folder and pull out just the icons for the monsters that might show up in the environment that my PCs are in in the session I am about to run and just move them into their "niches".
Now I can see everything I might want to use in a couple seconds. If the PCs head into (say) the necromancer's palace, I can look over at my laptop and take in all the options for who his guards might be or what might be chained up in his basement and choose something mood-appropriate.
I can take a screengrab of it and say Ok, this is the monster array for The Isle of Oth or whatever.
If I really feel like wasting time I can do it for every single environment in my campaign I can think of. Could be a pip...
Anyway I used this visual "category" method the other day and it worked pretty well. It takes some time, but tracking down all the monster pictures was fun, and it seems like a decent re-usable shortcut. If you don't have a laptop or a computer near where you play you could do a screengrab and print it out.
So I can see this basic idea being good for keeping track of traps or other widgets, too. Like Shiro has pictures of actors and actresses corresponding to NPCs in his Pendragon Campaign--you could have them all lined up by location or power-level or whatever so when you GM you're ready to go.
It might make sense to do it with a dungeon or world map, too, if you had a lot of elements on it that were going to get moved around a lot and re-used...
Telecanter's silhouettes might be a good place to start if you want to put together your own monster collection.
I also made some generic pictures and threw together an all-purpose lair...
...so no matter where the PCs go, if it's somebody's hideout I've got somewhere to start. I can stock it quick using the monster categories picture and roll...