Johnny Cash at the Great America Theme Park in Gurnee of all places.
Glen Campbell at the Taste of Chicago.
Luciano Pavarotti before he got thrown out of the Lyric Opera.
There are probably more dead opera singers, but I can’t think of any by name at the moment.
Jani Lane - singer of 80’s hair band Warrant.
Michael Hutchence - singer from INXS.
Adam Yauch (MCA) - Beastie Boys.
Jam Master Jay - Run-DMC.
Steve Clark - guitarist from Def Leppard.
Derek Frigo - guitarist from Enuff Z-Nuff.
Phife Dawg - A Tribe Called Quest
Bernie Worrell & Junie Morrison - George Clinton & Parliament Funkadelic
Peter Steele - singer of Type O Negative
Scott Weiland. It was a pretty crappy concert since it was promoted as “Purple to the Core” implying they’d play a lot of music from that era but around half was new non STP stuff and the only hit he played that was a favorite of mine out of the 8 or so he could have was Big Empty.
Clarence Clemons (solo)
Jerry Garcia (with the Grateful Dead)
George Carlin
John Denver
Glenn Frey (with the Eagles)
John Entwistle (with The Who)
Chris Squire (with Yes)
Pete Seeger
Ray Thomas (with the Moody Blues)
David Bowie
Chris Squire (Yes)
Hughie Thomasson (The Outlaws)
Clarence Clemmons (E Street Band)
Tommy Makem
The Clancy Brothers
Martin Fay and Sean Potts (The Chieftains)
Walter Becker (Steeley Dan)
I’m sure there are more, I’d have to think a while on what concerts I’ve seen over the years.
He was a cool guy. From Wikipedia:
He was a great guy, who had a hard life. He specifically wanted a hotel room with two single beds. He even had a specific distance he wanted the two beds to be from each other. When he went to bed, he slept in one bed and he laid his prosthetic leg down on the other bed.
To quote David Bromberg (?) You’ve got to suffer if you want to sing the blues.
Prince
Dennis Edwards
Bernie Worrell
Ray Davies
P-Nut Johnson
Bob McCallister
Almost forgot: Tom Petty
John Denver, Mitch Hedberg, John Hartford and more bluegrass musicians than I’m willing to list.
Arthur Lee of Love
Daevid Allen and Gilli Smyth of Gong
Mary Hansen of Stereolab.
I saw Wilko Johnson on his fairwell tour when he was ‘terminally’ ill. But he didn’t die.
I also saw all the great late 20th century Scottish pantomime dames on stage in the 70s and 80s - Fulton, Logan etc (Baxter’s still alive).
Prince, Tito Puente, Al Jarreau, Bobby “Blue” Bland, Maurice White (of Earth, Wind & Fire), Charles Neville (of the Neville Brothers).
Oh yeah, Dave Brubeck.
I saw The Dubliners in 1992/3.
I think I might have seen Angus Grant of Shooglenifty playing with the rest of the band in the street once.
Oops! Sorry, Carl!
I saw Mitch just before he cashed it in. A mere shadow of his earlier self. 
I was at Senna’s first F1 race. Getting kinda beyond the question, though.
INXS (Michael Hutchence); I saw them as part of a festival at RFK Stadium back in the early '90s.
Hey, Gato, if you wanna make a stink, Cozy Powell died in 1998, so you’re half-right.
You owe me a Coke.
Have you been listening to him for years? And do you think he’s fabulous?
I saw Marvin Gaye and Miles Davis the same summer, same park.
Stephane Grappelli
Johnny Cash
Waylon Jennings
Doc Watson and Merle Watson (saw them at McCabe’s Guitar Shop in Santa Monica)
Bo Diddley (opening for Jerry Lee Lewis who, like Keith Richards, is still alive, surprising everyone)
Ibrahim Ferrer (from Buena Vista Social Club); (would have been more enjoyable if the two women in
front of us hadn’t sung every song along with him).
Saw live, though not necessarily in performance:
Mae West - Getting out of a chauffeured limo in Beverly Hills in the '70s. She was overdressed and must’ve been wearing at least ten pounds of make-up.
Fred Astaire - Nearly ran him over.
Katharine Hepburn - Ate some sandwiches she made and hung out with her for several hours.
Robert Vaughn - At the peak of his fame in the late '60s. He was short.
Robert Stack - I was leaving work and some dude opened the door. I thought it was for me, but it was actually for Mr. Stack who was coming in to film a segment of Unsolved Mysteries.
Alan Napier - Alfred the butler on the Batman TV series.
Alan Hale, Jr. - In a restaurant back East somewhere.
Julius Sumner Miller - In performance. Julius Sumner Miller - Wikipedia
If you mean the lead singer of The Kinks, he is not dead. At least not as of the moment I am typing this.
If you mean Ray Davies, the big band trumpeter, than carry on.
Antonin Scalia.
…what? He came to town for lectures on two occasions, so I saw him twice.