'What the hell kind of name is soap?'
'How did a muppet like you past selection'
Thats my favorite, but I also like when the Russian gets a sawed off shotgun in the mystery box he says "this is the gun I used to kill my first wife."
I also like in MW2 when the guy freaks out (I think spetsnaz) "ENEMY AC130 ABOVE!!!!!!!!!"
EDIT: Nvm, my favorite is, "50,000 people used to live here.... Now its a ghost town.... I've never seen anything like it"