A camera would be pretty awesome, but you know what I'd like to see? An infrared remote control, like the one that you use (and can never find) on your television. You could then use the Vex system to do things you wouldn't want to whip out the big radio for, like having a robot open up a bottle of root beer* and send it down the conveyor to your couch.
Beyond that, a simple e-stop button to connect to the tether port would be kinda awesome. (The spec is already on the VexLabs site--it's just grounding two pins on the tether port.)
*Hey, you can have the thing open whatever you want--I'm just underage. 