Posted By:
PaulThe Zeenut of Fatty Arbuckle biting a baseball would have to be at the top of my list.
The Old Judge Whitney w/ dog is a nice conversation card, and so are the Old Judge mascot cards (Ewing w/mascot, Williamson w/mascot, the mascot by himself). There's also an Old Judge of "Long" and "Short", who I assume were among the tallest and shortest players of their time.
Other good conversation pieces are cards of Chuck Connors. He is in the 1952 Mothers Cookies set, the 1950 Big League set, and the 1950 Cuban Acebo set.
I think an M101-4/5 of Jim Thorpe also might start a conversation with a non-collector, as long as they knew something about sports.