Everything by David Gilmour before Waters left the band, everything before the highly uninspired 'Division Bell' and 'A Momentary Lapse of Reason' albums.
I'll just pick the guitarists who have been the most influential to me as a player, and my favorite solos from each.
Alex Lifeson - my favorite guitarist, so the list of great solos is vast, but the solo that says the most about his style is from Ghost of a Chance. Pure, beautiful, jagged emotion.
Jimmy Page - Totally agree with the No Quarter reference from Song Remains the Same, but how about The Song Remains the Same from Houses of the Holy?
Nuno Bettencourt - Phenomenal player. Rest in Peace shows why.
Brian May - Play the Game. That sound. Ooooh, that sound.
Eddie Van Halen -
Beat It
No kidding. If you can stomach listening to a Michael Jackson record again, give it a spin. Incredible technique, incredible soul.
John Petrucci - Pull Me Under - 'nuff said.
Eric Clapton - Pretending It'd be fashionable to go with something from Cream or the Dominoes, but this solo is as good as anything he's ever done.
Chris DiGarmo/Michael Wilton (Queensryche) - Revolution Calling - I love Maiden but these guys took harmonizing solos to the next level.
Elliot Randall - Do It Again - Though I'm not familiar with much else he's done, this is one of the all-time great solos in rock history, and my favorite from one of my all-time favorite bands, Steely Dan.
Steve Howe - Siberian Khatru - His work here is so evocative and atmospheric I still get the chills 25 years after hearing it for the first time. Just an incredible player.
I purposely left jazz/acoustic guitarists off my list becasue it seems this has turned into a 'rock' thread. I could just as easily have thrown out names like Kottke, Ralph Towner, Metheny, etc.
Likewise, I excluded instrumentalists like Vai, Satriani, etc. They're incredible, but because they're largely instrumentalists, their solos seem to blend into on another for me.
I thought about it but it seemed a bit too obvious and I like some of his other works better, such as Stone Cold Crazy.
Tony Bourge of Budgie (Here's a band that received far too little notice here in the states) - Breadfan - SkyHigh Percentage - Who Do You Want For Love - In For The Kill - Zoom Club.
Anything by Angus Young of AC/DC, especially the Highway to Hell/Back In Black/For Those About To Rock...
The guitar solo from Bob Seger's "Like a Rock". That slide guitar will give you goosebumps(I pretend Chevy never used this track for commercials).
Also, another underrated guitarist, Billy Gibbons of ZZ-Top. I remember reading once that his band prior to ZZ-top opened for the Hendrix Experience and that Jimi himself was blown away and reluctant to take the stage following Billy.