Three, actually. Normal version of Oblivion for the PC, and the disk is still at my parent's house (with the PC I used to play it on.) Even though the computer probably wouldn't run it anymore, and I'm not home enough to enjoy it anyway, I couldn't bear to throw away/ sell the disk. It's got a nice fat manual and pristine map with it still.
When I got my xbox one of the first things I did was buy a copy of Oblivion. I had to buy this second hand because I couldn't find a new one
anywhere. It was just the normal version because I couldn't find GOTY. This pre-owned copy came with a manual but no map.
Then when the 5th Anniversary Edition was released I went and bought it without even having to think twice about my decision. I wanted the Knights of the Nine expansion and knew it came with the anniversary edition. This came with a lovely, fresh-smelling map of both Cyrodiil and the Shivering Isles, plus a DVD. So I use the Anniversary disk.
Near xmas my friend wanted to play Oblivion for his xbox again so he could finish off all the achievements, so I wrapped up my pre-owned xbox copy and gave it to him as a present. He was delighted. So I guess I only have two copies now.