Comfortably Numb (Delicate Sound of Thunder) - Pink Floyd. I might have heard The Wall track first on the radio but I owned this album first, so it became the default version for me. As I was new to this genre, I wasn't used to songs lasting more than 4 minutes, or having such an extended guitar part. Someone asked Guy Pratt if playing this with David so many times over the years it ever became just another song. He said "nope, when the solo starts, I still get goosebumps."
2112 - Rush. I've said elsewhere (but cannot find to quote myself) a friend in high school told me to listen to this song. I'd never seen a song this long before. But he was usually spot on in recommending me stuff. After it was over, I had no idea what the hell I just listened to. But it was the most amazing thing I'd ever heard. In some respects it still is. One of my gateway songs in to my love for 70s/classic rock.
Sloop John B - The Beach Boys. No real good story here, but I came to love it during what was indeed the worst trip I'd ever been on. Internet says "Brian Wilson hired 13 musicians to record this song during a 12a-3a session on July 12, 1965."
Don’t Follow - Alice in Chains. Was never a grunge guy, which made me a bit of an oddball in high school growing up in the heart of it. But this song moves me more than almost any other to this day.
Gethsemane (I Only Want To Say) - Jesus Christ Superstar (1970). This was the most mind-blowing vocal performance I had ever heard at the time. The whole album, between Gillan and Murray Head, was just an onslaught of vocal ass-kicking. I know many other have tried to hit those notes, some may have even done it better. But this recording is still tops in my book.