Call of Duty, I refuse to use anything but: Mauser karabiner 98 kurz [http://world.guns.ru/rifle/rfl02-e.htm]
My other favourite weapon is the shotgun from Alien versus Predator 2.
It's not special in any way, except that it's secondary fire mode fires slugs [http://en.wikipedia.org/wiki/Shotgun_slug]. It's one of the few games I know to have slugs.
Of course, slugs in the game are meant to be armour piercing, but they are so rare and powerful I saved them for a 'real' threat. I have never finished that game, but they're so powerful I wouldn't consider a queen [http://images1.wikia.nocookie.net/avp/images/a/a1/Promo08.jpg] to be enough of a threat to 'waste' slugs on.