A .45 ACP Carbine would be cool -
the requirement that I would impose on it would be that it would accept .45 ACP handgun magazines, ie, are interchangeable.
I want my mags to be used by as many guns, interchangeably, as possible.
But my late-night 'oh crap, what was that' weapon is the bedside companion, a .40 S&W Taurus OSS with decocker, single or double action. Holds fifteen and one up the spout. The decocker allows a chambered round in a hammerless pistol so there is not even the clicking of the hammer going back or the thumb safety disengaging on a 1911. Eats hollow points or flat nose without a hitch.
The Taurus OSS DS in .45 ACP is also very good for reliability and effective wound infliction. It also comes with a decocker and you can get it with night sights. There is also a rail for a laser, should you want one for off hand shooting.