The memory grows thin as the head grows thick, but here goes:

The Who (twice before anyone died)
Little Feat (twice before Lowell George's death and three or four times after that)
Jimi Hendrix (once before he died and none afterwards)
The James Gang
Emerson, Lake and Palmer
Quicksilver
Ten Years After
David Bowie
The Band
Bob Dylan
Procol Harum
John Prine (at least three times)
Jesse Winchester (three or four times)
James Talley
Guy Clark
Jerry Jeff Walker
The Lost Gonzo Band
Asleep at the Wheel
McKendree Spring (I know, these guys are right up there with Lothar and the Hand People)
The Allman Brothers
Jackson Browne
Crosby, Stills, Nash and Young
Jesse Colin Young
Poco
Bruce Springsteen (three times -- once in an audience of about two hundred before his succesful third album)
Dixie Dregs
The Moody Blues
Amazing Rhythm Aces
New Grass Revival
Tom Petty
Steve Young
Jimmy Buffet
Continental Drifters
Rolling Stones
Tina Turner
Pure Prairie League
Booker T and the MGs
The Meters
Mavis Staples
B.B. King
Earl King
Chris Thomas King (and also under his real name Chris Thomas when he was in his teens)
Tabby Thomas
Larry Garner (many times -- this the best least known contemporary blues songwriter)
Raful Neal
Kenny Neal
Guitar Kelly
Johnny Adams
Clifton Chenier
John Campbell
Rockie Charles
Booker T. "Slopjar" Lowry
John Lee Hooker (twice)
Luther Allison (maybe the greatest guitar player and performer I ever saw -- gone too soon)
Ma Rainey II
Memphis Slim
James "Son" Thomas
Charles Brown
Buddy Guy
Allen Toussaint
Dirty Dozen Brass Band
The New Orleans Nightcrawlers
Rebirth Brass Band
Little Rascals Brass Band
Muddy Waters
Robert Lockwood, Jr.
Silas Hogan
Furry Lewis (saw several times, usually as a benefit to help him recover from a fire to his house or to get his guitar out of the pawn shop.)
Mississippi John Hurt
R. L. Burnside
Junior Kimbrough
Shemekia Copeland
Dr. John
Coco Robicheaux
Danny Barker
Galactic
Snooks Eaglin
Beausoleil
D.L. Menard
Eric Clapton
Irma Thomas
Sonny Landreth
John Hiatt (avec the Goners)
David Lindley
Steve Winwood
Steve Miller
Ry Cooder
Randy Newman
Oliver Mtukudzi
Femi Kuti
Tabou Combo
Hugh Masakela
Taj Mahal
Olu Dara
Keb Mo
James Cotton
Robert Cray
The Fieldstones
Zachary Richard
Eddie Lejeune
Marc Savoy and Ann Savoy
Balfa Toujours
Henry Butler
Eddie Bo
The Bluerunners
Buckwheat Zydeco
Rocking Dopsie and the Zydeco Twisters
Beau Jocques
Boozoo Chavis
Nathan and the Zydeco Cha Chas
Etta James
Bo Dollis and the Wild Magnolias
Sammy and Sandra Sandoval
Corey Harris
Albert Collins
Hubert Sumlin
Eddie Kirkland
Rufus Thomas
Ernie K-doe
Paul "Wine" Jones
Son Seals
Lonnie Brooks
Gatemouth Brown
Koko Taylor
Katie Webster
Henry Gray
Ronnie Earl
Anson Funderburgh and the Rockets (with Sam Myers)
John Mooney
Bobbie Rush
The Neville Brothers
Roy Orbison
Cassandra Wilson
Dianne Reeves
Max Roach
Charlie Byrd
Dizzy Gillespie
Thelonius Monk
Anyone named Marsalis
Marcus Roberts
Irvin Mayfield
Los Hombres Calientes
Mark Whitfield
Steve Masakowski
Terence Blanchard
Nicholas Payton
Abby Lincoln
Hadda Brooks
Stephane Grappelli (avec the Martin Thomas Trio)
Leo Kottke
Earl Scruggs Revue
Paul Simon
Delbert McClinton
Johnny Clegg
Majek Fashek
The Radiators
Warren Zevon
Doc Watson
Richard Thompson
Lyle Lovett
Daniel Lanois
Van Morrison
Lou Reed
Funkadelic
Fats Domino

and a bunch of classical performances.