Wow! SO many I want to list; many of my very favs have already been named. All of the following have bee SO incredibly formative to my life. Undoubtedly, I'll need to revisit w/ those I forget in my haste. ...

... Some of those I believe that are yet unheralded(?), that I'll apply a lil rapid~fire listing, include but are not limited to:
Les Paul
John Coltraine
Thelonius Monk
Etta James
Gram Parsons
Townes Van Zandt ...

... my brotha ...
Lowell George
Lightnin' Hopkins
Mississippi John Hurt
Otis Spann
Sonny Boy Williamson(yes, 1 and 2)
Junior Well
Big Joe Williams
Charlie Patton
Elizabeth Cotten
Scott Joplin
Buddy Guy
Louis Prima
Louis Armstrong
Edith Piaf
Dusty Springfield
Peggy Lee
Dinah Washington
Benny Goodman
Glenn Miller
Artie Shaw
Robert Johnson
Leadbelly
Screamin' Jay Hawkins
Spike Jones
Bob Wills
Hank Williams
Bill Munroe
Sam Cooke
Eddy Arnold
Nick Drake
Joe Strummer
Buddy Miles
Dicky Betts
Duane Allman
Peter Green
Janis Joplin
Vivaldi
Lizst
Beethoven
Tchaikovsky
Hmmmmmmmmm ...

... Then, I'd echo some of my other deceased favs I believe were all already saluted in this thread:
Mozart
John Lennon
George Harrison
Stevie Ray Vaughn ...

... My brotha ...
Hendrix
Jim Morrison
Johnny Cash
Patsy Cline
Nat King Cole
Frank Sinatra
Billie Holiday
Roger Miller
Bing Crosby
Nina Simone
Miles Davis
Marvin Gaye
Otis Redding
Howlin' Wolf
Willie Dixon
Billy Preston
Muddy
Zappa
Robert Palmer
Kurt Cobain
John Bonham
Freddie Mercury
Marc Bolan
Mike Bloomfield
Keith Moon
John Entwhistle
Richard Manuel
Layne Staley
... There are so many more ...
... Would be so fine to have them ALL chartin' as contemporaries in the now; what sound!!! ...