I've thought something like this

http://ruger.com/Firearms/FAProdResults?function=famid&famid=19&variation=.357%20/%209mm%20Convertible&bct=Yes&type=Revolver

would be handy - handle .38, .357, and 9mm. It's single action, but still. Probably not your main combat firearm, but...Did I mention that it's a single action cowboy type revolver - extra style points. Unless your all about the tacticool. Not that there is anything wrong with that. *sniff*