I like the Goldmine Fox. I will chime in with a few:
1948 and 1949 Sommer & Kaufmann
A card sized scorecard issued in 1982 in South Korea to commemorate a tour by Aaron, Ernie Banks and a few others to celebrate the opening of SK's first professional league.
All of these are just about impossible Jackie Robinson cards:
1950 Sylvan Sweets mail response card
1950-ish publicity mail response card
1955 All American Sports Club premium
Very tough regional Koufaxes:
It took me years to get examples of these:
1964 Penafiel (Mexico) Gehrig:
1950s Coney Island Arcade Gehrig:
This one is unique: