Not counting the NFA stuff that Dad bought before 86 and then registered, probably this unfired Norinco 56S-1 with the accessories and original packaging from the 80's, which I inherited from Dad.
I had one of those that I bought in the 80's for around $200. I wish I had bought a dozen! Mine came with a high capacity banana magazine, can't tell if yours did too. My friends and I had fun shooting it a few times. I traded mine a couple of years later for an Italian made Beretta 92 that was for sale at $650. I thought I had made the deal of the century.

To me, it is funny that many of the guns listed here are military surplus ones. When I bought my Mosin Nagants, SKS's, and others, many years ago, I never imagined that they would increase in value so much! Like most people here, I wish I had bought many more stacking them deep. I remember contemplating buying a full crate of the Mosins. Of course, years ago, the Mosins that were for sale near me were in much better shape than the ones I see for sale now. I had dreams of removing the cosmoline from everything, putting it all back in the crate, andd lighting, and making a coffee table out of it.
Larry