Some wonderful names been mentioned - many of which would be on my list.
I have been lucky enough to have seen (in no particular order)
Ike & Tina Turner (1960s), Townes Van Zandt, Dominic Behan, Muddy Waters, Lowell Fulson, Henry Red Allen, Gene Vincent, Chris McGregor's Blue Notes and his Brotherhood of Breath, David Olney and many more.
                                                                Lucky enough to have bought Big Joe Turner a tin of throat pastilles.                                                       Lucky enough to have been bought whiskey by both Freddy King and B.B. King.

Who I would love to have seen would include (in no particular order):-
Billie Holiday, Elvis Presley (1964-66), Gary Stewart (sadly departed and much under-valued honky-tonk singer), Charlie Mingus,
Louis Armstrong (preferaby 1927.......), Joe Ely Band of late 1970s (with Ponty Bone, Lloyd Maines and Jesse Taylor), oh and loads more.

I'll no doubt think of more.