Sheriff upright Nintendo is rare, only 2 or 3 known in the world, although probably the same with the Sega version. It's a shame as it's Nintendo's best looking cab imo, would love to see some more found so I can get one lol.
Atari Popeye is a rare one too - the fact Alpha1 still can't get one with all the cabs he's found over the years is testament to that I think!
There's gonna be stuff pop up that people didn't know existed at all, things keep showing up you just didn't think was made. There's also a lot of collectors who just won't reveal the rareties they've got in their collections, or just don't visit the forums. I think there's a ton of guys like that out there, with cabs that have probably never been seen by anyone else.