I don't really know who would be the "most" famous. I've had some odd conversations over the years.
I speak to Pirates' FO (Hurdle, Huntington, Coonelly, Nutting) every year.
Nomar (across aisle on a flight from Dallas after he injured his arm vs Texas)
Bobby V. (had an adjacent table at his restaurant following the Todd Pratt HR game vs Arizona. Ralph Branca also there, but didn't talk to him).
Jason Robards (was really polite to my wife , but mostly ignored me at some restaurant that no longer exists)
Paul Newman (offered to buy my girlfriend a beer while I was filling up my car at a gas station in Westport, didn't invite me)
Bob Novak (bizarre conversation about Scott Peterson case on a plane)
James Carville (often spoke at a grocery in Alexandria)
George Will (conversation about Mussina trade morning after it happened at a National Airport bookstore)
Ed Rendell (his photo op at our store to "support local businesses")
Dick Durbin (epic half hour baseball conversation with a sprinkling of Obamacare thrown in during campaign stop at our store, love this guy)
George H.W. Bush & Brent Scowcroft (at Cape Arundel GC while they were getting ready to drive to first tee and we were held hostage by Secret Service. Amusing guy, that Bush. But the SS guys were a real scream.)
Odd thing is, with all the pols on this list, I've never been in politics.