I could have sworn I'd already chimed in on this, but as is evidenced by my lack of stellar prose, I see that it, like just about everything else, slipped my teflon mind.
Anyway, my top five, in descending order of greatness:
Genesis, World Tour '77, Oakland Colleseum. Same concert as is mentioned in Vax's post, for very much the same reason. I was too young to truly appreciate it, and it STILL tops my list.
Santana, at the Tabernacle, 2000. One day before my back surgery. To say the man was on fire would be a monumental understatement.
Dixie Dregs, 2005. A swingin' concert in a very personal setting. They were so hot they confused the computerized lighting system. They were on fire, they were up tempo, and they left the place a smoking crater. One for the record books.
Pink Floyd, 1992. Even though they didn't do much from DSoTM, it was still one of the best concerts ever. I sat on the downwind side of the stadium and got a contact high like you wouldn't believe.
Yes, Masterworks tour, 2000 (or was it 2001?). All old stuff. Nothing shorter than 7 minutes, and aside from one song, nothing shorter than 20 minutes. Their version of Ritual had the entire audience swinging from the rafters. Their version of Starship Trooper, as opener, started out with a bang, and "And You And I" was punctuated by some very close lightning. They really know how to put on a show.
Honorable mention: The Moody Blues, not because they were so hot, but because the lady I was with was.
Roger -Dot- Lee, OK, so they did a VERY good job, I just wasn't paying that much attention.