Legit albums or can I include bootlegs/singles/EPs/etc?
If I get to include bootlegs, it'd be Tori Amos, followed closely behind Radiohead and Pearl Jam.
I have close to 150 Tori albums/cd singles/bootlegs.
If we're talking just full-length albums (studio albums, not live stuff like the releases that Tori and PJ put out of their entire tours), I'd venture it'd be U2, Rush or Ozzy (including Sabbath). Motorhead and NIN would be close behind, tho. The longevity/output of those artists is incredible and I have every official release by those artists (I just don't know off-hand who would win out).