Does anybody make the simplest USB device possible?

I'm looking to get hold of the simplest USB device possible.

All I want the device to do is do the handshaking with the machine, 
nothing more. I want to use the device as a physical configuration token 
for some software I writing, so that the user can plug in or remove the 
USB device to affect the software in a nice physical way, rather than 
messing around with configuration settings. I'm considering finding the 
cheapest USB device that I can, but it would be much nicer (and I hope 
cheaper) to have a device designed for the purpose, particularly since 
the cheapest USB device I've found so far was a keyboard!

Does anybody know whether such a device exists (preferably in a range of 
colors), alternatively does anybody know how I might go about get one 
made and how much I should expect to pay?

Thanks,

Tony Wright.

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