Shotguns... A uncomplicated joy in our hectic world. Here's my list of some of my favorite Boomsticks :-P
1) XM2014 (crysis), *stealth, stealth, stealth* SURPRISE!! *BOOM, BOOM, BOOM!!*
2) AA-12 (MW2), This gun + extended mags + scavenger perk = Walking meat mincing machine. Awesome fun in close quarters :-D
3) USAS12 (MW3), The first shotty available and arguably the best. Has range, power and a great mobility. Running the rats nests of the mp maps with this little beauty can be a blast.
4) SPAS-12 (BLOPS), My favorite gun of the mp. Mainly because it's range and power wasn't nerfed by putting on a silencer. Quiet, deadly and just a little sexy.
5) Dinner Bell (Fallout: New Vegas), This is a unique variant of the hunting shotgun and obtained upon completion of the quest "Bleed me dry". In addition to the gun, you also get to bed its previous owner. A intense woman by the name of Red. Everytime I fire it, I hear her call out "Oh daddy" and smile :-)
Please feel free to add your own, theirs plenty more out there :-D