I will be doing this with Dark Souls, but I have also done it with both Legend of Zelda Ocarina of Time and Star Fox 64 (and their 3DS re-releases). I've bought Resident Evil 4 at least 3 times between the GCN, Wii, and 360 releases. I've bought Halo 1 and Halo 2 twice each as well...
I bought the N64 Paper Mario at least 3 times, because I kept being stupid enough to trade it in and then, within a few months, be yearning to play it again. That was dumb of me. But it taught me a good lesson about trading in games, and how I should just never do it. Ever. Hehe.
Edit: Oh, I've also bought the Diablo II battlechest twice.