Every Bethesda game after Daggerfall, minus Skyrim.
Morrowind: Bought it, it died, bought another copy.
Oblivion: Bought it, realized getting GOTY edition would be cheaper than getting expansions piecemeal, bought GOTY.
Fallout 3: Bought it, realized getting GOTY edition would be cheaper than getting expansions piecemeal, bashed myself on the head for falling twice on the same mistake, bought GOTY.
Skyrim: Bought once, am now waiting for the realization that GOTY will be cheaper than getting expansions piecemeal.
Also, I think I've bought about 5 copies of the original Mass Effect. This game is pretty unlucky for me, I've managed to destroy the disk in every way from it melting due to nearby objects catching fire (really) to my dog eating it to simply scratching it.
Batman Arkham City. Didn't realize I had to upgrade to XP service pack 3 to play it, so I bought another copy having decided my first didn't work. Boy did I feel stupid that day.
Looking through my game collection, and for whatever strange, strange reason, I seem to own two copies of the first Harry Potter movie tie-in game. I have no idea what those are doing there. I don't think I've ever played either, and I don't recall buying them.