Top five live Rock And Roll Albums

"Live In The Air Age" - Be Bop Deluxe
Far superior to any of their studio recordings with a version of "Adventures In A Yorkshire Landscape" that is positively beautiful. Sonic quality is right up there with Humble Pie's "Rockin' The Fillmore". You can actually hear the space. Great stuff. 

All of the others mentioned here I agree with to one degree or another, but it's very difficult to give one credence over another. The re-issue of "Ya-Ya's Out" a couple of years ago is well worth duplicating part of your collection. 

Every time I listen to "Waiting For Columbus" I get royally pissed off that Lowell George died. Damn. 

"Nighthawks At The Diner" - Tom Waits
Where most people including myself started with Tom Waits.  An American Master indeed.  One of the very few artists who's new releases I buy without reservation.  

"How The West Was Won" - Led Zeppelin.  
This is the sh*t, period. Dayum, those guys were good.  The later live releases suck by comparison. 

Dave Brubeck Live At Carnegie Hall
i can still listen to Blue Rondo here and be amazed at the mad skills involved. 

SOME live albums are indeed a cash-grab, but as many do manage to capture the vibe of an artist's performance - like most of what lenmc2964 began this thread mentioning. 

Lucinda's Fillmore recording is a perfect example of how a live performance can energize a song. "Change The Locks" is an exercise in tone shift - the studio version strikes me as almost timid while the live version seems to emancipate.  It's a riff that Crazy Horse could be proud of as well. 

So far as 80's hair/metal bands go...well...

Live jazz recordings are an obvious exception - this is where those guys live.