The AR-15 thread is interesting, but lots of folks here may not want to spend 1 oz AU to get a nice one. Here are my suggestions for those who are not into tacti-cool:
Shotgun: Any brand name pump action 12 gage shotgun. A must have for home defense IMHO. Hopefully that unmistakable "Clack-kachak" sound of chamber a shell ends the disturbance without a shot.
Handgun: A .357 mag or 38 Spl revolver. The basic cop gun that served law enforcement for most of the last century. I like revolvers over autos for two reasons. First, because there is no manual safety to remember to flip, the safety is a link inside the gun that prevents the hammer from striking unless the trigger is pulled back. Second, autos are more sensitive to ammunition because it has to automatically feed. Mid range caliber hollow points may or may not expand and that versatility in ammo lets you shoot some nastier non-expanding bullets like semi-wadcutters.
Rifle: Some in the AR-15 thread mentioned the Mosin-Nagant rifle. I have one, like it and they can be bought for less than $100. If you want a little more rapid fire in a handy carbine I would consider a classic 30-30, the classic American deer rifle that most hunters have upgraded from (might find one less than $300 used). If you live in an urban area like I do, you might also consider a pistol caliber carbine like a Hi-Point. A lot of hard core gunners dis them, but my model 995 is about $250 new, shoots inexpensive 9mm ammo, has never malfunctioned and has a 100% warranty for the life of the gun.
Good luck to all, hope things never slide this far downhill.