I was at a local con recently (
www.ogc-con.com) and I ran some Call of Cthulhu adventures (the classic system, not that d20 garbage). The adventure started with a professor at Miskatonic University giving a lecture on pre-Christian cults. During his lecture, he's supposed to go insane, rip out his eyes, throw them at the attendees, and jump out a window, killing himself.
Here's what I did....
My wife is an expert in making molds and castings, and she made me a very realistic set of eyeballs, even down to my eye color. She also made some latex "flesh strips", blood-red of course. I also had a tube of fake blood.
I put the eyeballs, the flesh, and the fake blood in a fanny pack, and kept it at the small of my back, with my t-shirt over it so as to cover it up.
When I role-played the professor, I put my hands behind my back, making it a natural action characteristic of some lecturing blowhard. As I droned on, I reached into the pack, got my hands nice and red, and palmed the eyeballs, one in each hand.
At the right moment, I began screaming, put my hands up to my face, made a fake ripping motion, and hurled the eyeballs onto the gaming table in front of the surprised players.
Unfortunately (or fortunately), there was no nearby window for me to leap out of. The unforseen benefit was that my hands were stained with blood for the rest of the session, a fact that some players found "unnerving" but in a good way!
Definitely my favorite prop!
Second favorite prop: My Midnight Syndicate CD that has a D&D soundtrack. Some of the music is absolutely perfect for mood setting.