On my "active gaming" shelves: Original D&D + Supplements, 1e AD&D
On my "reference" shelves: Holmes, '81 B/X, '83 BECMI and RC
In storage boxes: 2e AD&D, 3.0 D&D, Castles & Crusades
Never bought 3.5, 4e, or Pathfinder (and have never played Pathfinder).
Oh, I also have copies of OSRIC, Swords & Wizardry, & Labyrinth Lord. The first two are on my "reference" shelves. Labyrinth Lord I gave to my eldest son (high school), so I guess it's really his, not mine. He's been running a game for his friends for the past couple years. They play twice a week (!) during the school year and about three times a month during the summers. Oh, to have such free time!