Props can go a long way toward adding realism and enhancing the atmosphere of your game. I am a big fan of props and try to incorporate them whenever possible. Here’s one I’ve gotten to use recently: The Echo Mic.
The Echo Mic is just a simple plastic tube shaped like a microphone housing a spring or coil of metal. When you talk into it, it adds a metallic echo to your voice. You won’t win any Oscars for Sound Design with this thing, but its cheap and relatively effective (mileage may vary depending on the quality of your voice acting).
The Echo Microphone is most useful for creating ghostly, eerie, or otherworldly voices. The cries of the undead, the distant moans of zombies, the voices of ethereal beings, etc., are all good candidates, enhancing the atmosphere of a room or encounter or giving weight to an important NPC. As an example, I recently used it to help roleplay the character of Sir Keegan in Keep On The Shadowfell, emphasizing his ghostly dialog. It can also be used to create unusual sound effects by tapping the sides or rapping it on a table.
You can find his prop for just a few bucks at a party store, toy store, or online retailer.