Mine might be from another generation...
Bob Dylan - probably 15 times
Tom Petty & Heartbreakers - once (with Dylan)
Willie Nelson - once (also with Dylan)
Joan Baez - once alone and again in the Rolling Thunder Revue
America
Seals & Crofts - twice
Poco
Eagles
Jimmy Buffett (opening for Eagles)
Jackson Browne - twice
Paul Simon - once (with Dylan)
Harry Chapin - twice (shook his hand & got his autograph)
Bruce Springsteen
Neil Diamond
Roy Orbison
The Captain and Tenille
Danny and the Juniors
Jewel (opening for Dylan)
Janis Ian (took picture with her & got autograph)
Jesse Winchester
Arlo Guthrie - once by himself and he also came on stage briefly during the Rolling Thunder Revue in Springfield, MA)
New Kids on the Block (this one was for my daughter; she was 8 at the time)
Marky Mark and the Funky Bunch (ditto the above)
There are probably some I've forgotten, too...