Well, firstly is Kiss, since I own every album on CD, all the 70's and most of the 90's albums on vinyl, plus about ten cassettes.
2nd is Pearl Jam, what with those crazy bootlegs. Plus I collect CD and vinyl singles from the band too. Then there are a few cassettes.
I also own every album from lots of other acts, like Metallica, Megadeth, Iron Maiden, Led Zeppelin, Hendrix, and Pink Floyd.
I have to say, if I wasn't blowing major cashage on stupid articulated plastic, I'd be headlong into obscure vinyl album collecting.