I've got a few things:
1. Solid Snake. Kills tanks with hand grenades, camouflage suit... Plus some awesome stealth skills and combat abilities.
2. Raiden from MGS4 or Ninja from MGS1. I guess Ninja, since he blocks bullets with his sword.
3. Ezio/Altair, but I haven't played the games.
4. Big Daddy or Big Sister, but I haven't played the games.
5. Gordon Freeman. Everyone forgets the Tau Cannon from HL1... ^_^
6. Doomguy, since he KILLED HELL!
7. Necron Lord, except he'd kill me. It's in the job description.
8. Sarah/Infected Kerrigan. Psychic ninja or Psychic warlord.
9. Any Chaos God from Warhammer, although I don't think they appear directly.
10. Alex Mercer. I think he's technically indestructible. But he'd probably kill me by mistake. Seriously, I've seen him kill civilians just by walking down the street.
11. Cole MacGrath (Good), since he'd just electrocute everyone, and revive me if I was shot.
12. Cyberdemon/Spiderdemon from Doom. Consider yourself pwned.
13. Gandalf, in Return of the King game. At level 20.
14. The Swarm from Resistance 2. How many people take 3 industrial sized nuclear reactors with them on an assassination?
15. A Bug from Starship Troopers (it had a game). Just for scare factor.
I'd finally go for Ninja, Cole or The Swarm. Swarm for silly, Ninja for ninja, Cole for generic bodyguarding skills.