DOOM's SSG is a fantastic example, but I just might go with Duke Nukem 3D's shotgun when the chips are down. It feels right. It. looks right. Using it in combination with Duke's boot is awesome.
Honorable mention to the Mossberg 500 in Rainbow 6 Vegas 2. It fired fast and was very dangerous out to considerable distances.
Coincidentally, the Mossberg in 'cruiser' configuration is what DN3D's shotgun is based on.