If you had access to a time machine, what concerts would you go back to see?

1972 - Genesis at the Castle, Columbus, OhioStands out among all others in my life. Gabriel in full costume changing for each song and telling stories between each song.Collins with a drum kit from 200 years in the future.Rutherford, seated the entire concert with a rack of 8 guitars behind him, giving a master class on nylon-stringed guitars. One of the most vivid memories of my life.

1973 - Miles Davis at the OSU student commons in the round. He walked among us playing a keytar (don't know if it was called that back then but he was one of the first).

Quadrophenia Tour 1973 was awesome. Almost as good as Elton John and John Lennon at MSG. Early Springsteen at Asbury bars and small theaters compete.
 Would love to have been at Monterey, Bangladesh and Last Waltz (even the movies were outstanding) but did get to see all nights at No Nukes, Dylan 30th anniversary (all good but Bob), Concert for 9/11 and all nights at Rock N Roll Hall of Fame 25th anniversary shows --all at MSG. 

@artemus_5- I saw Rossington Collins Band 3 times during '80/'81. Shows were incredible. Last performance was at a 2500 seat theater. My buddy and I were standing right in the front center of the stage and had our arms on the stage floor. He took photos. Watching Allen Collins rip into the solo for Freebird (they did an instrumental version at that time), and dance across in front me so close I could have touched his legs was a moment I'll never forget!
Buddy Holly- Last performance w/Crickets Oct. 3, 1958, Worcester, MA Auditorium (I grew up here)
Beatles- I'd like to have been in London and witnessed the rooftop concert
Hendrix- Savile Theatre London, June 1967 with McCartney in attendance-he performed Sgt. Peppers (song) 3 days after it came out
Lynyrd Skynyrd last concert w/ Ronnie Van Zant, Greenville SC 10/19/77
Zeppelin- MSG
Elton John/John Lennon -MSG
Any Deep Purple show 1972-1973

Great post! Without question U2 Live at Red Rocks 05, June 1983! What an amazing experience that must have been for those who were fortunate enough to attend. U2 at their primal best (IMHO) just before they truly hit the map. Then they just got too popular and mainstream and got all weird on us...Too bad as early U2 man, that's just some DAMN GOOD music!