Pink Floyd - the second band I was really into, after a fling with Oasis, and the first band whose complete catalogue I bought but eventually I branched out into other classic rock and I pretty quickly left them behind once I was getting new music pretty rapidly. Still can't stomach listening to a full album. I actually got into and out of these guys before I ever smoked pot.
Roxy Music - junior year of high school I loved these guys and thought Bryan Ferry had the richest, most luscious voice in rock. Once I put on For Your Pleasure at a party and the less said about that the better. Older and more tuned-in to subtlety I find a lot of their music almost unlistenable because of Ferry -- although to be fair his voice is perfect for some songs and even albums.
Belle & Sebastian - was really into them around 2005-06 and got their discography on vinyl because, y'know, vinyl. I don't think I really need to elaborate on why I fell out with this group; anyone who was into them in college knows what I'm talking about. I also thought the pictures in the album art had something to do with the band so I didn't know the girl singer was a land whale until I watched the DVD from the deluxe version of The Life Pursuit.
Honorable mention to Jethro Tull; they were my favorite band once (and first concert) but I got sick of them though we parted on good terms: I still enjoy their music whenever I put it on. Just off the top of my head; there are certainly others.