Bob Dylan - Pure legend , one of the greatest song writers. His voice isn't the same as it used to be but still would like to see him before Dylan isn't around anymore.
Seen him twice, he still rocks. TOTALLY worth it if you ever get the chance, funny voice and all.
As for me... I'm not really the "OMG I WOULD DO ANYTHING ON EARTH TO SEE ____ PLAY LIVE" type. But these are the bands that I haven't seen and would be... hmm... extremely enthusiastic about seeing, if they played anywhere close by:
D.T.R
Rock'n Roll Standard Club Band (no idea if they ever even performed live...)
X Japan
Loudness (original lineup, or if by some strange chance it were to happen again, 1992 lineup with Masaki and Taiji)
Seikima II
Cloud Nine
Kings (good luck...)
really any of the major '80s Japanese metal bands
Buck-Tick and Luna Sea, "for old time's sake"
And yeah, that's all Japanese bands, because I've already seen most of my American must-see bands:
B'z (OK, they're Japanese too)
KISS
Aerosmith
Poison (twice)
Motley Crue
Bob Dylan
LA Guns
And if I could build a time machine:
X!hide, especially during the "Hide Your Face" era
Johnny Cash