JohnS wrote: just a Remington 870 18 inch pump 12 gauge loaded with #7 birdshot and equipped with a Surefire tactical light on the foregrip right next to the bed.
Why the shotgun? Reliable, extremely effective, and the sound of the pump action being racked will very likely end a home invasion before the gun needs to be used. The grip mounted flashlight means I don't have to fumble around with a flashlight or risk blinding myself temporarily when flipping on the inside lights.
Why #7 birdshot? Because it is perfectly capable of taking someone down at the close range of a home invasion, but the shot will not penetrate multiple walls and siding like a pistol or rifle round will, which means if I miss, I'm not going to accidentally kill a neighbor with the stray round.
I'm not advocating one position or the other (I enjoy sport shooting very much, but don't own a gun, and don't have plans to own one, but wouldn't mind owning one, more for sport than for protection. . .you get the picture, I'm not solidly on either side), but my father-in-law, who has many guns, advocates the shotgun as the preferred for home protection. It's (1) relatively easy to operate; (2) the pump sound is distinct and gives fair warning; (3) not only is birdshot less likely to injure innocent bystanders, but it's also more likely to wound an intruder rather than kill, and (4) birdshot scatter makes it easier to hit the intruder.
For those who chose a gun for home protection, this is sound advice, I think. You're also less likely to shoot yourself with a shotgun.