#1 - MacGyver - I can't believe there was never a pin made for ol' Angus MacGyver. Sooooo many possibilities.
Honorable mention:
Huey Lewis and the News - I own BTTF but there is only 2 Huey songs. My personal best of compilation is at 46 songs and that is the abridged version.
ZZ Top - Once again BTTF only has one of their songs, but they top AC/DC, and Metallica in my opinion. This would be a pin that I would break the bank to order NIB.