I saw Coldplay a few years ago in Toronto and it was incredible. U2 before they REALLY got old in 2002 was a solid 9.9/10. I just wish I were older to appreciate it better.
Alexisonfire at Welcome Week 2008 was also really really awesome, and I've also been in some pretty awesome concerts with my own band
On the other side of the coin, Mindless Self Indulgence was just brutal. I like their music, and I used to listen to it 24/7 (for about a week), and when I saw them live, I partially knew what to expect, but it was just really really loud, some nut punched me in the mouth because he thought I was a bear, and I personally don't like being berated by a band for giving them my money for what they called a "shitty expose of terrible music".
I believe the last line of the night was: "We won't play an encore because only s**tty bands who care what you think play encores and we aren't that, so baibai." Cool.