Mine would have to be my ST:WOK pendent Khan wore in the film. It's made of brass and aged. It's stamped "1982 Paramount Pictures" on the back. It's also my oldest.:cool
When I was doing my now-illegal and unethical Smallville Kryptonite keys, I ended up making some 1/2" versions that fit in a model of Clark's ship that was being made at the time.
The medium key in the pic is the accurate prop version size.