My problem with the Chili Peppers live is that Anthony Kiedis cannot sing. He can write a song like a badass but his voice is like torture when he sings live. Still a badass show.
I've seen a bunch of bands. Metallica; Pantera; Ozzy; STP; Aerosmith; Staind; Korn; all sorts of country music acts; and way too many local bands to even begin to start listing them, among others.
But I saw a band called Reveille http://en.wikipedia.org/wiki/Reveille_%28band%29
at an Ozzfest one year. They were on the second stage, in the middle of the afternoon, and no one had ever heard of them. I picked up a CD of theirs months before on a whim at a store (yes, they used to have those) and simply adored the rap/core angst at the time, and some of my friends enjoyed it too.
So, we didn't even realize that they were going to be playing the second stage when we got there, ended up forcing our way to the front of the second stage before they came on (not too hard between bands) and started rocking the hell out. Well, I guess Reveille didn't have many fans because, as I was banging my head along with each note and singing along with each lyric, at some point during the show each member of the band acknowledged me and my three friends standing in front, climaxing with the lead singer letting us get some mic time. It was a unique pleasure.
After the show the guys were literally walking around during the rest of the day long festival, and I recognized them straight away, as they did me and my group of friends. We talked, partied, hung out for an hour or so before they had to leave for the next show. The band broke up soon after this but, besides local shows that were just really fun because I knew everyone there, this was my favorite time at a concert ever, even if it wasn't the most fun or the best music.