USB Missiles are fun (I shot Dvorak in the chest with one once, it did not induce a heart attack as I had hoped), but actual cannons are even more fun. This 25-inch field cannon is the closest you'll get to having a Civil War cannon in your office—unless you're the undersecretary of Civil War reenactments for the State of Virginia.
It's powered by gasoline and flint, which means you can actually fire "real" ammunition from its turret. US$149 gets you the gun, and you'll have to buy separate flints and ammo for about US$10 each. The thing also weighs 3 kilos, which means that in the worst case scenario when you run out of ammo you can just throw it at someone's face. [LighterSide via Nerd Approved]