Not including bands that I've seen live in concert of actors or singers I've seen on stage..Probably the most famous I've met were:
Leonard Nimoy (very nice... I was 10 at the time, so Spock was God to me...)
John F. Kennedy Jr. and wife (not very friendly, but cordial..only a few months before their deaths..)
Buzz Aldrin and wife (he was very nice, his wife was freaky)
Gene Cernan (last man to walk on the moon) (very nice)
James Acheson (well-known film designer, including the upcoming Spider-Man flick and 'The Last Emperor' -- chatted for 15 minutes about Terry Gilliam movies)
John D. MacDonald (mystery writer)
Milan Stitt (writer, "The Runner Stumbles")
Bob Kane (creator of Batman, and stuck-up egotistical asshole)
Maryann Talese (opera singer)(and bitch)
Piper Perabo ("Coyote Ugly" "Rocky and Bullwinkle") (went to school with her, she's mostly nice...)
...too many Marvel and DC Comics people to mention.. tons of them...
The following don't really count as meeting them because I didn't converse with them or shake their hands...
Princess Margaret (seen from about 30 feet away)
John and Norma Major (seen from about 100 feet away)
Liz Taylor and Sen. John Warner (in Paris... actually they did say hello back to me and waved, so I guess we met...)
Don Knotts (shopped in my store a few times)
Jimmy Nelson (famous ventriloquist, ditto)
There are probably more I'm not thinking of...