Thought it'd be time for a poll on this. 
DISCLAIMER: Duke Nukem isn't on this list because 1. every character on this list has a recent game and 2. Duke Nukem Forever has made the king of manliness fall out of grace with me.
Now of course, I haven't played every game so obviously there are going to be some characters missing that probably should've been on it, but hey. This list will have to do I suppose.
So, the choices are:
Marcus Fenix, Gears of War
Known for his grunty voice, immense muscles, time done in the goriest, crappiest prison imaginable, wielding of firearms with chainsaws attached and a hard time showing affection towards anyone.
Shown here in the middle:
The Master Chief, Halo
Known for getting things done guns blazing, speaking only when something needs to be said, wearing armor that weighs more than a humvee, travelling through space on the back of a nuke.
Brucie, GTA IV
In Brucie's own words: "Cars, check. Body, check. Paper, check. We're winners baby! That's HOW WE ROLL UP IN THIS
. Man I'm so jacked up, I gotta hit the weights!" Known for ordering people wasted because of 'roid rage.
Shown on the right:
The Doom Guy:
Known for his lack of a vocabulary and being the only person to succesfully stand up to a demon invasion and kicking them back out. Also known for being the only non-female character to sport a uniform that leaves room for the showing of abdomen.
Captain Price, Call of Duty 4
Known for an extensive military career including sniper missions in Pripyat, attempting to avert nuclear disaster and the tieing down and beating up of terrorist mastermind Al-Asad. Also known for casually smoking a cigar on a blackhawk helicopter moments before insertion on a terrorist freighter in the middle of a Bering Strait storm.
Gordon Freeman, Half Life
Known for instantly turning from scientist to super hero after the chief moment of disaster, complete lack of a vocabulary and skill with a crowbar. He may not have the most masculine appearance of this list but that doesn't seem to stop him from being a juggernaut of death.
Kratos, God of War
I've never played the game myself, so I'm not sure what he's known for. I would say he's known for kicking boatloads of ass in melee with swords and claws and hooks and whatnot, despite the fact that he entirely lacks armor of his own. He is bald because he's too manly to bother doing his hair. He appears to have a chain melted into his arm, something that most would consider a handicap but Kratos sports it like a tattoo.