I personally have to say Johnny Cash “Live at San Quentin”
I might agree with some other albums in this thread, but Rush’s Exit…Stage Left certainly deserves a mention.
The Concert in Central Park. Simon and Garfunkel rule!
I liked An Evening with John Denver as well. Okay, so call me old-fashioned.
Four Way Street
Crosby, Stills, Nash & Young
Bob Dylan, “Live at Budokan”
Another vote for “Live 1966” by the Folksinger Formerly Known as Bob Zimmerman. You get both an acoustic/solo and an electric/full band set, and you get to hear some angry English guy call Bob Dylan “Judas” for daring to play one of those newfangled electric guitar thingies.
“Live Dead” by the good ol’ Grateful Dead is also excellent! The classic 20 minute-plus “Dark Star” followed by “St. Stephen” followed by “The Eleven” (so named because the time signature is 11/7). Then you get Pigpen wailing away on “Turn on Your Lovelight,” “Death Don’t Have No Mercy,” some spacey jamming, and an a-capella “We Bid You Goodnight.” An excellent example of the original Dead lineup in their prime.
There are also a number of other live Grateful Dead CDs, released under the “Dick’s Picks” banner. (Dick Latvala was the long-time keeper of the band’s tape vault) Of course, it is also possible to get almost any Grateful Dead show on an audience tape, since the band was kind enough to allow Deadheads to record and trade tapes, as long as no money is made off of it.
I guess with a name like “Jerrybear,” it was inevitable that I would mention Uncle Jerry’s old band.
Hmm, I’m willing to concede the possibility that the Allman Brothers Live at the Fillmore is worth considering. (You can tell the folks who are on the bus by whether they smile at the cry of “Whipping Post!” or not.) Ditto for the Who Live at Leeds (“Maximum R&B”). Some of these other mentions are just odd (um, Michele, we’re talking live albums).
Dead Can Dance – Towards the Within
Éire Óg, Live at the Brazen Head … probably an acquired taste though.
Yo. We gotta talk. 
** 4 Way Street**. Dear me, I forgot about that. This IS troublesome. Small world item: The photography in that album, as with many other CSNY/CSN/CN albums is by Joel Bernstein.
His kid sister was my first great love. 
MC5 - Kick out the jams, anyone? Personally, I think Bad Religion’s Tested is pretty good as well, but the setlist is a bit mediocre for their standards.
Yo back atcha 'toon!
While we’re at it, Coast to Coast by BR-549
The Yellow Shark by Ensemble Moderne
Live in San Francisco by Tabla Beat Science
Okay, not totally prog, but cut my teeth on it.
Frampton Comes Alive!
OOPS! Disregard my answer! I misread the thread topic!
I’ll second Nirvana Unplugged in New York.
10,000 Maniacs Unplugged is also great!
Guns N Roses Live Era, followed very closely by Cheap Trick **At Budokan{/b]
One From the Vault The Grateful Dead
Hard to believe it’s over 30 years old: Stones - Get Yer Ya-Ya’s Out
And, from around the same time: Hendrix - Band of Gypsys
Warren Zevon - ‘Stand in the Fire’