I have one custom card - an In Memoriam Lyman Bostock that I got through the blogosphere.
I think a set of athletes / war veterans would be cool if done right.
Multi-sport athletes.
Athletes who were elected to office.
Jackie Robinson
Willie O'Ree
Glenn Burke
Don Johnson (as a power boat racer)
Carl Weathers (He had a couple bank-sponsored cards, but no major releases.)
I saw the best cards of my generation destroyed by creases, soft cornered hysterical edge wear, dragging themselves through the hobby shops at dawn looking for a top loader...