Most famous, I would say, would be Buzz Aldrin. Very nice and cordial.
Duffy Dyer held a door open for me when I was a teenager. I had no idea who he was. (Catcher for the NY Mets.)
I've met a few professional wrestlers: Rick Flair was nice, Tazz stayed in character, Missy Hyatt was very nice.
I've met some Beatles related musicians. Pete Best was fairly friendly, Billy Preston was nice, Donovan is a wonderful person, Laurence Juber and his wife Hope (daughter of TV legend and Gilligan's Island and Brady Bunch creator Sherwood Schwartz) couldn't be nicer, Mark Hudson (of the Hudson Brothers) is friendly and hilarious, Neil Innes (of Monty Python) is also swell. The late Victor Spinetti was great, as was the late Zacherle (Chiller Theater, etc.). Harry Nilsson was also very nice. Mark Rivera, of Billy Joel's band, also a friendly, funny guy.
Oh, and when I was a little kid on a family vacation we met the legendary reporter Edward R. Murrow, who was gracious.
Everybody I know who has met Paul McCartney sings (pun intended) his praises.