Let's see...I have this terrible feeling that this list is going to be entirely RPGs and I'm going to emerge from it feeling distinctly unmanly.
Pokemon - I'm not sure it counts, since I rarely play through the games more than once, being meticulously careful to craft what I consider the ideal team on my first run-through. Nevertheless, Pearl currently has about 150 hours clocked on it all by itself, and I've played FireRed at least five or six times.
Oblivion - Too much. Way too much. 100+ hours logged on my primary character alone, and I have an additional five in various stages of completeness.
Fallout - Seven or eight play-throughs, I think.
Fallout 3 - Four play-throughs and about 200 hours in total.
And then, the granddaddy of them all... Diablo II. Maybe not in terms of play-throughs--I played battle.net, so basically I just made two Paladins and a Necromancer and I was up and running--but in terms of physical time spent leveling, dclone hunting, Ubering, farming, and fuck-all else, it easily consumed more than a thousand hours of my life. Probably much more.
Mmm, yeah, that's what I was afraid of...all RPGs. Time to go get my testosterone pumping with a manly manly shooter like TF2.