There was a time when the only game I owned was Super Mario Bros. for the Nes. I bet I beat that game somewhere in the neighborhood of 100 times. We used to play two player and bet on who would beat the game first. I've even purchased multiple versions of the game over the years and still beat it on a regular basis.
I've also beaten games like Zelda LttP (got my time down to three hours, at one point, I think), Super Metroid (I think I got my time down to less than 1.5 hours if memory serves), Resident Evil 1, and Chrono Trigger (beat New Game plus so many times, my characters were level **).
In recent times, that title probably goes to Metal Gear Solid 3 or Resident Evil 4.
This gen? Probably Tomb Raider Legend (which I also bought on PS1 and PSP) or Gears of War 1--both on the 360.
