Allman Brothers, Portland Oregon, fall of 1991 -- they were two hours late to the venue, refunds were offered, band finally came on, apologized and said they were going to play everything for us. Which, damn sam, they did, for almost four hours.
Little Women, Portland Satrycon, 1992, Drug-edgey jam band usually played the regular 'alternative music' club, but on the night before I left for D.C., they played the hardcore punk club and kicked it out of the park.
The Verve, 9:30 Club, November 1997, loudest show I can remember, band was on fire with the noise, and I spontaneously made out with the girl standing next to me during the 'Come On' freakout.
Guided By Voices, 9:30 Club, last year (August?), my first time seeing them and it was so great that I couldn't stop laughing the whole time.
Grateful Dead, RFK Stadium, 06/25/95, the last D.C. show, and after 61 previous shows through the years, the best I (and my partner of 40+ shows) had seen. Then Jerry died, which was probably for the best.
Honorables:
that last Black Rebel Motorcycle Club show was seriously great.
I thought the Immortal Lee Country Killers II, opening up for the Driveby Truckers a few months ago, were just about perfect.
Monster Magnet at the old 9:30 Club was insane.
The Verve at the old 9:30 Club in 1995 was incredible, mostly due to the ridiculous amount of tension between the singer and guitarist. Great bootleg too.
Soundgarden, Monster Magnet and Swervedriver in Seattle in 1991
Pavement at the old Black Cat in 1994 has always stuck in my head, as has the Afghan Whig show there a couple months later.
Worst Ever Show:
The Dude of Life at the old 9:30