Pretty much any RPG I've ever played. If I pick one up again, I'll just keep playing it, coming back day after day until I'm done. One of my flatmates started playing Dragon Age recently, so I ended up starting again, and then thought I'd see how the story changed if I did certain things differently, and then... Stupid immersive game
Golden Sun's bad for this too (both of them) - every time I stumble across them in my house, I feel the urge to see how quickly I can get through the game. Subconsciously, I might be losing them around the house deliberately just so that I rediscover them from time to time...
This extends to the pokémon games, even though they lack the story element that usually drags me back.