Rock:

Monterey Pop Festival - better than Woodstock, or at least it is judging by the footage in the movies. Otis Redding and Jimi Hendrix's performances are two of the best I've ever seen, by anyone.
Bob Dylan - The concert in Manchester when someone called him "Judas." Fantastic concert, there was footage of it in that Scorsese documentary, and there's the CD that has the entire concert (or most of it, not sure if it's complete).
Pink Floyd - The Wall, in '80 or '81.
Isle of Wight Festival - The Who, Miles Davis, Jimi Hendrix, etc., although not as good as Monterey Pop.
The Sex Pistols - That famous Manchester concert, I think it was in '77.
Pink Floyd at Pompeii.
Parliament/Funkadelic - Any show on the Mothership Connection tour.

Jazz:

Benny Goodman Big Band vs. Chick Webb Orchestra - sometime in the mid 30's, there're no recordings, but it was supposed to be killer.
Count Basie vs. Chick Webb - the very same night of Benny Goodman's 1938 Carnegie Hall concert (which also would've been cool, after Gene Krupa saved the band), Basie left after the jam session and headed over to play against Webb.
The Quintet at Massey Hall, 1951 - Bird, Dizzy, Mingus, Bud Powell, and Max Roach. The CD recording is a classic among classics.
Duke Ellington - Newport, 1956: another classic. Paul Gonsalves' famous 27 chorus solo lasts around 10 minutes.
Bill Evans - the Village Vanguard, '61.
Monk at the Five Spot, during the period when Coltrane was in his quintet.
Charles Mingus at the Monterey Jazz Festival in the early 60's.


Those are all the specific concerts I can think of, I'll add more if I can think of them.

I'd love to have been at the Motorhead gig at the Birmingham Town Hall that actually caused structural damage to the building it was that loud. My mum claims she could hardly hear Hawkwind who played after, but also claims that was not necessarily a bad thing.

Lollapalooza '93. Tool and Rage Against the Machine and Alice in Chains... Mmm.

Deep Purple came to a city close to me, as did Pink Floyd, I wish I'd seen them then.

i'd have loved to have been at any so-cal punk shows in the early 80s. so many good bands sprung from there.

Ramones - CBGB's

Nirvana MTV Unplugged...

i would've liked to see their first show with television at CBGB's. that would have been awsome.

*dies*

Seriously?

Yes.
In all seriousness.

OH NOEZ. Shoot her. She likes blink. Poseur.

:)

Nah, I know they were utter shite live, and there was no technical skill at all to them, but dammit they were fun. I loved them to bits, and still like to listen to a lot of it.