+1 on the .38 revolver/12 ga pump bandwagon.

The only meaningful thing I can hope to add (so far everyone's advice has been excellent) is that addition to the racking of the slide, the barrel of a 12 ga is pretty intimidating in and of itself.

Also, realize that a gun is useless if you don't know how to use it (train with your tool), is useless if it isn't handy (make it accessible to you), and deadly to YOU if you don't secure it properly (take proper precautions to secure your weapons so if you walk in on a burglary in progress the criminals aren't armed with YOUR weapons).