Due to my age, this doesn’t compare with some of the historic posts - Woodstock?! Cool!! - but for me, it was Lollapalooza, July 15th 1994, the Chicago homecoming for Smashing Pumpkins. It was a great line up with L7, Nick Cave, George Clinton, Beastie Boys, then the Pumpkins finally appeared and opened the set with “Cherub Rock.”
The place went absolutely insane. Local gang made national headliner.
I wish I could remember which opera it was, but sometime in the 80s I saw Luciano Pavarotti and Jessye Norman together at the Met. The singing was of course spectacular . . . but I remember wondering how the stage could hold those two huge bodies at the same time.
Offhand, I’d say Pink Floyd doing “Careful with that Ax, Eugene” when I saw them in '72. Brilliant and chilling.
A few others:
Ali Farka Toure in concert in Bamako, Mali in 1995. Hot, sweaty place, but nobody really noticed that as he tore the place up.
Buffy Saint-Marie singing Now That The Buffalo’s Gone in Carnegie Hall in about 1967. I had front row seats.
Ray Charles singing Georgia On My Mind at Wolf Trap in 1992.
I was privileged to see Amalia Rodriques’ last concert. It was in Lisbon, and even though her voice wasn’t what it had been, just hearing the world’s best ever fado singer was wonderful.
I saw a band called the Lee Boys do “Voodoo Chile” with Warren Haynes on guitar. I think the video from that night is floating around on YouTube.
I’d have to think about it…but Wednesday I saw Ben Folds and YMusic do “Erase Me” and with the horns and strings it sounded fantastic like a 50’s spy song
It wasn’t a Rush concert without “Closer To The Heart”. There was one show I attended where they stretched it out to about 10 minutes, and could have continued. 
The first time I saw Alice Cooper and he sang “Billion Dollar Babies.” It blew me away. And of course, “School’s Out” and “No More Mr. Nice Guy” weren’t slouches either, but the former is what I’d been waiting for forever.
Leonard Cohen doing “Hallelujah” live was a literally religious experience.
But the best ever would be one of those bands you’ve never heard of, Tuatha Dea, who were running overtime and finished the show with a cover of “Zombie” that ran right into “White Rabbit”…at double time. Exhilarating doesn’t begin to describe it. I didn’t have a drop of alcohol or any illicit substances, and I felt higher than the proverbial kite.
Syd Barrett was one of the founding members of Pink Floyd. He became mentally unstable & departed from the band in 1968. He released 2 solo albums. During those sessions, he did a song called “Word Song” which was eventually released in 1988. It’s a product of a profoundly damaged mind. It’s just a string of random words sung plaintively with a guitar strumming alongside. In other words, it’s completely unreachable for the audience. It’s as abstract and remote a piece of music as has been written.
In 2007, I was lucky enough to be able to attend a Syd Barrett tribute concert at the Barbican theater in London. One band did “Word Song” as a giant sing-along with the audience. They had the words projected behind them, so you could follow along. And, everyone did sing along. It was genuinely magical. I was moved emotionally as never before at a concert. The band had the audacity to completely redefine the song. No longer was it a song of exclusion, of loneliness, of pain. Now, it was a song of inclusion, of joy, of wonder.
You can see a video of this exact performance here. It was filmed from the upper level & I was on the floor. Maybe that’s why you don’t hear as much of the audience. But, trust me, it’s playful and I wish you could’ve been there!
My first concert was Welcome to my nightmare. The songs all stood out, I vaguely think I can remember what it was like to hear “I’m 18”
I saw The Who in a relatively intimate (4,000 seat) venue in 1980. Had great seats.
Daltrey was in fine voice and Townsend was very energetic. I will never forget their performance of ‘Won’t Get Fooled Again’.
mmm
Daft Punk doing One More Time at Coachella ('07?). The debut of the pyramid.
Saw Page/Plant in the mid-90s, and ‘Ramble On’ stands out to me as the most memorable song I’ve ever seen live.
I can still see the explosion of lights when Plant belted out “A-RAMBLE ON!”
Beachboys doing Johnny B Goode, Bangor ME 1963
Paul Butterfield doing Johnny B Goode, U of Maine gym, 1971 maybe.
Stones doing Monkey Man at stadium concert 1994 Madison WI
Oh yeah! Sorry to pipe in so much.
I saw Aerosmith “Back in the Saddle” tour opening shows at the Orpheum, one of them New Years Eve. It was the reunion of Joe and Steven. The whole place was pitch black and the lights went on with the first notes of “Back in the Saddle.”
Wow. Never thought of it like this. I’ve been to a lot of great concerts, but picking one song?
I saw Adrian Belew perform at a little ~300 ppl) club the day after Roy Orbison died. At the end of the show he played a Roy song or two in tribute. I remember ppl pushing the tables and chairs off to one side so they could dance to, “Pretty Woman”. One of the more fun, spontaneous moments I can recall. If you get the chance to see him in a venue like that, do it. Intimate is the right word. It was like hanging out in his game room while he jams and tells little stories. He had just got some sort of stereo effect, so at one point he decided he’d play around with that for a bit. Very informal, very enjoyable.
Musically, maybe the best song was Roy Buchanan’s, “The Messiah Will Come Again.” Beautiful.
I’ll go with Frank Zappa, “Inca Roads,” Beacon Theater, New York City, February 1988.
Really tough to choose a single song. The best show I ever saw might have been Doc Watson and Jack Lawrence in a bar that barely held 300 people, but I couldn’t pick out one song that stood out over the rest of the show.
As for a single song, I’m going to go with Richard Thompson (electric) doing Tear Stained Letter. It’s a good song and Thompson’s an great guitarist, but multi-instrumentalist Pete Zorn is every bit his equal on saxophone and when the two of them get going at the same time it’s incredible. It was a couple of years after this (and the audience didn’t suck when I saw them), but it was a similar feeling. If you don’t want to build up to it, you can skip to 3:35, but the whole song’s worth it.
On a related note, Zorn must have played six different instruments in a 45 minute set. I went in really excited about seeing Thompson and I wasn’t disappointed, but I left raving about the whole band (ok, mostly Thompson and Zorn).
On a similar note (and with no way to identify any particular piece of music), Bela Fleck (banjo), Edgar Meyer (upright bass), and Victor Wooten (electric bass) playing… something indescribable and amazing.
This, and Colibri’s seeing The Who at Woodstock are…wow.