Bionicle: The Game.
Hey, I was eleven when I first got it, and Bionicle was my life back then. Give me a break.
I mostly bought new copies because of that CD key it came with. At that point, I didn't think to write CD keys on a Word document, so every time I wanted to reinstall it, I had already lost the key, so I would need to buy a new copy...just for the key.
Fortunately, it was only sold for fifteen bucks everywhere, so I didn't waste TOO much money. I still got a very healthy 1000 hours out of it.
(Mind you, that's a rough estimate. I've had the game in some form or another for about seven years, even though its not very good. I have a PS2 copy for nostalgia's sake.)
Other games I originally had for PC I sought out for PS2, since my computer was absolutely terrible at the time my friend gave me a PS2.
These include: Ultimate Spider-Man, Lego Star Wars 2, Lego Indiana Jones, Lego Batman, and some others I'm probably forgetting.
Now I've got a sleek, sexy, and powerful Gaming Laptop (thanks "Santa"!), so I COULD reinstall all those games for PC again...but I'm too lazy.
EDIT: Oh yeah, there was also Rise of Legends, an RTS and sequel to Rise of Nations. Again, that damn CD key eluded me, plus I lost the disks.