Torque bow and the chinsaw bayonet of DEATH(rippin through flesh while music from lamb of god is playing in the background) from GeOW

Gravity gun from HL2. Great weapon especially during the part when you would be in ?ravenstark (forgot the name...its a headcrab zombie town) and then using it to pick up the razor-sharp blade wheels in some rooms to rip them through the zombies

Finally (though this isn't a shooter), the True Ryuken A.K.A. the True Dragon Sword from Ninja Gaiden...or should I say Ryu Hayabusa? i mean the weapon is only as good as the one who wields it after all. nonetheless, bothweapon and wielder are very, very, very bad-ass (had a lot more fun with this weapon compared to the unlabored flawlessness)