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

@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!

Stevie Ray Vaughan Aug. 1990 so I could tell him not to get on the helicopter!!!!
AC DC 1980 tour I was there had a fabulous time on acid but did not have to opportunity to really remember the music.
Robin Trower at a small club in Madison
Rory Gallagher anywhere any time!

Hawkwind at the Treorgy Tree Festival, 1988.
I didn't attend because of personal factors. They played all of my favourites, including Assault and Battery and others from Warrior on the Edge of Time.

Alternatively the Stax revue that toured England in 1967, and played in West Hampstead at a dive known as Kook's Clique. It was a revelation for both artists and audience; Otis Reading, Sam and Dave, Booker T were the house band, and they had only played segregated venues in the US before.
 Years later they would say
"Play it like we played in London"

Also my parents were there, two years before i came along,  so that gig is part of our family story

@kingbr, great point about catching a band early in their career, before they go mainstream and sell out (assuming they even get that opportunity). Not to mention having to deal with the trendster - wannabe, "Johnny come lately" fans that show up once the band becomes mainstream.