A Thompson SMG that, at today's prices, would be worth tens of thousands of dollars. It belonged to the police department where my dad was sergeant. They sold it, and some other odds and ends, of to a machinegun dealer back before Ronnie Raygun closed the registry. I hope it is in civilian hands somewhere now.
Also handled, briefly, a Luftwaffe drilling a cousin of my dad's owned. He died unexpectedly and his sister inherited his extensive and expensive collection. She sold it en masse to a gun dealer who did a pretty fine job of boning her on every one of the guns. She knew nothing about their values, nor did she care, so she took his check and ran.