Weird - I have been thinking of starting a thread about people I wish I had seen, but no longer can. Now I see that someone did it four years ago.

A quick list:

Muddy Waters
Waylon Jennings
Johnny Cash
Cyril Tawney
Big Mama Thornton
Manitas de Plata
Clancy Brothers with Tommmy Maken (did see Liam Clancy and Tommy Makem in separate gigs)
Kenneth McKellar
Kathleen Ferrier
Pavarotti
Edith Piaf
Soviet Red Army Choir