I would not part with my right arm, but the two concerts I would most like to have seen were Bob Dylan at Manchester Free Trade Hall in 1966 and Jimi Hendrix playing the Haleakala Crater in Maui, Hawaii in 1970.
You can see footage of the Dylan show in Scorcese's No Direction Home, and footage of the Hendrix concerts in the motion picture Rainbow Bridge, though I don't know if that would be easy to find.
This is actually from Edinburgh, not Manchester, but it is representative:
This is not my favorite song from the Haleakala shows, but it is representative:
the ziggy stardust tour in the 70's....
and like iluvjeisa i would love to see GNR in the 80's..
jimi hendrix..rolling stones - mmm, the list goes on forever.
And sex pistols 1976 - 77...