Most times you've ever beaten a single game?

That would be Vagrant Story.  I've beaten it a total of 17 times.  It's still fucking incredible after all those times.  = D

I've played through all the Pokemon RPG's multiple times.

Man, I thought beating Half-Life 2 three or four times was impressive.

Does beating Eternal Darkness with the three slightly different stories count if it was a means to get the secret (real) ending?

all the metal gears several times and final fantasy X 4 times.
oh and a lot of the total war games dozens of times.

I've played Super Metroid countless times. So much so that over the years I've lost count.

Its to this day the only meaningful game I've played more than once, single-player wise. I haven't played it in a couple years though. Don't feel like hooking up my beat-up SNES anymore.

The original Rebel Assault, which I must have beaten at least two dozen times when I was a kid. These days, a game needs to be really, really special for me to play through it more than once. Fallout 3 and Dead Space are the only games I played through more than once in the last year and a half or so.

I've beaten Civilization Rev. about 10 times.

I've played through both Halo 2 and Halo 3 five times each.

Mass Effect 6 times, wasn't even aiming for achievments, was only time ive done that as usually twice is enough.

I've beaten GTA San Andreas 9 times.

Metal Gear Solid 3... I think I have about 56 playthroughs =\ I love that game...

Suikoden I & Suikoden II about 4 times.

Final Fantasy Tactics probably about 80 times or so.

Grand Theft Auto IV - 3 times, on my 4th play now

Well, if you count all the different ports and remakes, I've beaten Final Fantasy II/4 at least a dozen times over a decade. Bastards had my number with the Wii stuff...

Other than that, my second most would be Lufia II and the PSX Metal Gear Solid.I've played each at least 5 times through each.

I beat MGS4 5 times. 

When I was trying to speedrun Super Mario Brothers after I bought it on the Wii VC, I probably beat that game a solid 100 times.  I forget my best time.  It was nowhere near the best times on the net, but it was fast enough to super-impress my casual gamer friends, heh.

Has to be Super Castlevania IV for the SNES.  Must have beat it over 10 times.  More recently?  Dead Space at 3 times. 

Pokemon Blue 5 times, Mass Effect 4 times and Sin and Punishment 5 times.

half-Life 2, ive beaten that like 30ish times