I have a rough prototype of the ZVEX Communicator (TM, Patents Pending). It lets a musician communicate with the monitor engineer (or FOH guy in a small club) to relay needs for up to 4 channels... for example, he needs more vocals in his monitor and less kick, so he clicks one stomp switch to move the cursor to vocal and another stomp switch to select "more", "less" or "nevermind". It has little windows for four channels that are full of bright LEDs and illuminate a piece of artist's tape that has writing on it. One is in front of the musician, one in front of the monitor person.
It has other features too. Stepping on both switches illuminates an "emergency" LED which indicates "look at me!"
Hitting both switches 3 times resets both units in case of a crash.
It can send the signals through a mic cable up to 1km.
It can send the signals through a snake.
It has midi inputs and audio inputs with LEDs indicating signal presence, so that one can use CD backup tracks or Midi tracks that "click in" without telegraphing the click to the audience through the monitors.