Favorite gaming supplement

Hello,

I'm often on the lookout for cool stuff to make gaming better for my campaigns, and so I throw this question out to the site:

What is your favorite gaming supplement aid?

This can be anything. For my part, I really like a couple of Pathfinder products. The Ultimate Campaign book and their set of foldable dry erase maps.

What do the rest of you think are quality products that really help gaming? Inquiring minds want to know!

The Pathfinder Pawns are really handy if you want to have presentations for various beasties/NPCs etc.

Also there is a supplement I can't remember the name of but it dealt with big changes to a campaign world from a Meteor strike.
That supplement is pretty awesome if you want to shake your setting up.

When the Sky Falls by Sword & Sorcery

AEG's Toolbox circa early 2000s. Just a couple hundred pages of d20 rolls in tables for all kinds of amazing things. Dungeon dressing, adventuring party names, dog names, dwarf names, portents, random encounters...

I have to build a "add a random table" function at some point...

There is a real old boxed set Greyhawk cities and it had all kinds of city building stuff in it.

This.

The GM's Survival Guide for L5R had a lot of really good resources for GMs. From a lot of background information on customs, etiquettes, ceremonies, etc. for GM wishing to bring Rokugan to life further. List of occupation for peasants, type of animals and food found within the Emerald Empire, encounter table, list of village's names, etc.

mmm Rokugan

I've never played L5R the RPG, but I've heard people gush over the system.

It's an interesting system. It's a story of samurai drama, so don't expect your typical RPG tropes. Instead of gaining levels, amassing treasure, and getting sweet magical loot, in L5R, you instead acquire honor, glory, titles, and then try to have the most epic and/or honorable death.