Dang, lots of old stuff on here so for discussion's sake I'll throw something out there and let's see if someone takes a shot at it.
I know that many folks rely on their pistols and as an NRA Instructor and Training Counselor I know that the NRA's Personal Protection Inside the Home course is built around the use of a pistol but I would submit that for home defense purposes an 18" pump action smooth bore shotgun loaded with either single or double ought Buck is the optimum CQB firearm and load. In smaller homes where you would be shooting at distances of 9-12 ft. across a bedroom or down a hallway, you are producing a pattern of shot roughly the size of a good sized grapefruit and in larger homes where you may be shooting across a room or down a hall that is 18 to 24 ft. you will be producing a spread roughly the size of a soccer ball, all of which fits neatly within the size of a human torso.
Personally I prefer an 18" combat ported Remington 870 with a 2 shot mag extension, aluminum six spot side saddle, Mesa Tactical M-4 stock and pistol grip, Ergo three rail forend with a Surefire G2 light. The combat porting of the barrel greatly reduces recoil and completely eliminates muzzle flip so that sight picture is not disturbed and my follow on shots are far more rapid and on target.
