At the risk of this being a completely subjective topic, my short list (in random order):
Art Garfunkel
Josh Groban
Joan Baez
Freddie Mercury
Karen Carpender
Roy Orbison
I’m not a fan but it’s hard to question the beauty and quality of Babs and the height of her powers.
For pure velvet brilliance I’d go for Nat King Cole.
Sarah McLachlan’s voice can send shivers down my spine.
Chris Cornell, whose music I don’t always like, has the perfect rock singer’s voice and range.
Sandy Denny.
James Taylor.
Alison Krauss.
Steve Perry and Pat Benetar spring to mind. Why yes, I did come of age in the '80s.
Karen Carpenter. They gave her a lot of insubstantial crap to sing, but my God, her voice was magnificent.
ETA: sorry, I see she’s mentioned in the OP. Okay, then, Aretha Franklin and Steve Winwood.
Elvis.
Sam Cooke
Smokey Robinson
Aretha Franklin
Neil Hannon (The Divine Comedy)
And Annie Haslam.
Olivia Newton John
Barry Manilow
Elvis Presely. Could pretty much sing anything.
My votes…(yes, also a little 80’s-ish, and bending the definition of popular)
Harry Nilsson
Peter Murphy
Terri Nunn
Nena
Deborah Harry
David Bowie
Brendan Perry
Johnette Napolitano
Anyone who has ever had the life-altering experience of hearing Van Morrison perform live, on a night when he was “on” knows the answer to this question…
(on the nights where he is simply going thru the motions, it’s a bit of a different story)
Judy Garland
Frank Sinatra
Mario Lanza
Mama Cass
This is a tough one – for females, I would go with Olivia Newton-John, Sarah McLachlan, and Karen Carpenter.
Hopefully, I can think of more singers later!
Lots of good ones mentioned already. Allow me to add:
Roger Daltrey
Petra Haden (this video made the rounds a while ago)
I think Judy Collins deserves mention.
Greg Lake had a wonderful voice before he started declaiming instead of singing.
Tim Buckley had chill-inducing vocal power.
Neko Case
So did his kid, Jeff.