The 1911 is simple to maintain, effective and can often be obtained rather inexpensively (though they can get pricey for a nice rig). There's a reason the design is still so popular after 100 years...
It's VERY difficult for me to walk away from one if I have a reasonable chunk of cash in my pocket, but I do have a bad habit of picking up a new magazine whenever I see one. I usually have 2 or 3 clips loaded with 230gr. Hydra-Shoks lying around in my Jeep and at least half a dozen more around the house at any given time.
For home defense, a 12ga is hugely popular. It's ridiculously versatile and you can load it with anything from rock salt to dimes if 00 buckshot or a tungsten core slug aren't to your liking.
Now if you're talking about a complete collapse of civilization scenario, or if you're going to move out to the middle of nowhere a la Thoreau, you might consider an AIR gun http://www.quackenbushairguns.com/index.html. The nice ones can bring down game animals. Lead bullets can be molded over a wood fire, and as long as you can breathe you have air to shoot it (if you have no air for propellant, then shooting your gun is the LEAST of your problems).