Bands/artists you never got to see live in their heyday, but would've liked to.

I’ll go with Chet Atkins too.
Also Duke Ellington and Jim Reeves. 

I've actually seen a good deal of the artists mentioned in this thread. I saw almost all of the rock acts that are mentioned, with the notable exception of Prince. I saw Ellington -- a model of grace and charm. I did, though, miss Coltrane, Bird and Pavarotti. My older sister saw the Beatles at the Hollywood Bowl. She yelled herself hoarse. 

Queen   
The inventors of the modern light show.

Seen a Steely Dan show. With respect to Walter the newest Steely Dan Band is in another league.

monk
coltrane
clifford brown
bill evans
ella
eva cassidy
amy winehouse