Handguns in general, are bought in matching pairs. Gun number two should be an exact copy of gun number one.
Now gun number three should be what ever tickles your fancy right now, at this moment in time. If its another handgun, see above, as it will now be three and four.
This really is a very vicious disease, and will only get worse, and you will never be satisfied, so you might as well get used to it now, and get it out of the way. Hey, its only the kids college fund, and they're still young yet. Oh, screw it, let them fend for themselves! (trust me on that part, they will actually come out for the better in the long run if you dont cater to them, and you'll save bunches of money for more guns) Go for the SMG's next! Talk about addiction!!
While the above sounds a little silly, its really not all that far from the truth, and I do really buy my handguns in pairs, so I have an exact spare to practice with and rotate out, but thats me. Since you have the revolver, I'd look at one of the better brand name autos that catches your eye and feels good in your hand. Then double them up.
Personally, I think handguns are better than shotguns for use indoors. They are a lot easier to maneuver with and hold onto in close quarters and you tend to practice with them more too. Nothing wrong with one in a static, hold out location along with your handgun though. A nice little AK or AR is even better yet.
See, I told you it was an addiction.