Here are some idea's given that we aren't looking for ones that sideshow will inevitably make. I would start by looking a vehicle drivers, as I don't see many of them getting done. With that in mind...
First is Keel Haul, the admiral of the USS Flagg. Awsome figure and was one of my favorites as I was lucky enough to have the carrier. He is both iconic and would fit in nice with the other commanding officers.
Next, and sideshow may have mentioned interest in this character, Wild Weasel. Great fan favorite as the A10 Warthog was a unique plane with a Bad A$$ gun and the Rattler was a 'must have'. The quality of the Joe line improved a lot in '84 and Wild Weasel was immediately iconic in a lot of ways.
Captain Ace, Nuff Said.
Wild Bill, some great customs done already by Elvis will make you a believer.
Copper Head (Water Moccasin Driver). I don't think many would expect to see him, which in a way is like a sucker punch. (I like his colors and unique snakelike helmet)
Cross Country. Just kidding, I hated this figure as well as the HAVOC, even though I did own it.
Frostbite, Clutch, Hiss Tank Driver (V1) pretty much round out the list for me. Although Clutch was on the generic side, he holds a place for me as he was my first Joe in '82.