Favorite DMing Tools

Day 2 of the 30 Days of GMing Challenge: What are your favorite GMing tools or accessories?

Random Charts
As a game master, I really love random charts of all types. I don't use them all that often, and almost never at the table, but before hand while doing prep? They're fantastic inspiration.I especially recommend checking out other peoples random tables. There's lots out there to choose from, and don't be too picky either. It doesn't really matter if it's from the wrong genre, or the wrong edition of the game. It really doesn't. The point is to give you a jumping off point for your imagination.

Media: Books, Movies, TV shows, Radio/Podcasts
Consume all types of media in as wide variety of subjects as you can. You never know when a silly Bollywood movie, or a French documentary on pastry chefs, or a book on William the Conqueror, or a story on NPR will catch and link up with that episode of Star Trek or a song lyric from a Broadway show, or something from Nightvale and come out as something that'll be great at the table.

Notebooks
Lined, unlined, graph paper, digital, whatever. Any place you can scribble notes, maps, ideas, and sketches is a must have. You might want to try to keep from proliferating them too much, otherwise you'll never remember where they all are, let alone which idea is in which. You might also go the route of having a 3 ring binder or something where you can insert and remove pages as needed.

Dry-erase Markers and Battlemap
Even if you're not using minis to the extent that 4e needs, being able to sketch out areas for your players to see is always useful. Keeping it on the dry erase board has the advantage of forcing your players to redraw it themselves if they're doing their own mapping.

DM Screen and Dice
Now, I tend to do most of my combat rolling in front of the screen, but having the screen does allow me to keep my notes hidden, and roll dice for non-combat reasons. It has the advantage of amping up the paranoia of your players and helping to keep their focus.