I love using visual aids. Though I'd actually call them "physical" aids... for instance, in a fairly recent campaign I DMed, an NPC wanted to make a quick throw of his dice against the PC's throw. So as I roleplayed the NPC, I had two real dice palmed in my hand. I had went ahead and cut and carved 2d6 out of some scrap earlier that day. When the NPC offered the PC a chance to roll the dice, I actually handed the player the wooden dice.
Now, that might not sound too cool, but it was cooler than I nearly expected

The players at the table were actually
stunned, though we managed to finish that bit of RP before the questions: "Where'd you get those wooden dice? Did you make those? I didn't even see you holding them!"
Making a couple of crappy dice was easy, and hiding them in my hand, under the table for the most part, wasn't hard either. But the reaction was great, especially with the surprise value
I did a similar thing when I DMed I6 Ravenloft. For the scroll that the PC's find on the dead dude on the way to the castle, I went ahead and wrote it up on a piece of printer paper. I wrote it left-handed and cursive, so it didn't even resemble my handwriting. I did the standard tea-soaking, too. And since the guy was found in the mud, I added some of that, although I got the clods and mess off before rolling it and crumpling it. No need for dirt all over my table
I've done a few other scrolls, too. Wax seals, burnt sections of map, the standard stuff. I've maybe done it half a dozen time in a dozen years of gaming, but it's better that way because it's always better when it's a surprise
