Everyone should have a handgun (and train with it regularly). While a handgun is a compromise, often it's the best compromise for a given situation.

Everyone should have a rifle (and train with it, although it's not necessary to train as often as with a pistol). I'm partial to Modern Sporting Rifles (http://www.nssf.org/MSR/facts.cfm).

Personally, I have enough rifles and handguns for all the shooters in my household.

Shotguns are darn handy, and can't be beat for home defense from a static position.

If you're missing one of these, I'd suggest you'd start with what you're missing.