ORIGINAL: semi
9mm leaves you undergunned? hardly. It's not on the light side, i don't care what anyone says. Sure a .40 or .45 has more behind it, but with today's defense rounds a 9mm is pretty effective if you are trained.
i would suggest the Springfeild XD9. i have one, and its quite the firearm for the price. over 2300 rounds on mine without a single malfunction using Winny White box. This gun is a little big to carry so i have a 380 for that. But you have to decide if you are going to carry or not and let that be your guide. If you are just going to be plinking, get a .22LR pistol and shot 550 rounds for $12 instead of 50 rounds for $15 (9mm) or $22 for .40 cal. If you are looking for a defense gun there are so many choices but they all matter if you are going to carry. If there is any chance you will get your CCW and you don't want to buy a bunch of guns, you could look at Kahr, Bersa, or a revolver which should be 9mm or bigger yet smaller framed. Just go with what fits your hand best.
I would certainly plink with this, but most of my target shooting (as Ben would know) is done with my bow. I would have this to take along in my vehicle, keep at home, and of course shoot at our range at the cabin when the mood strikes me. The "do-all" gun definitely leaves out a .22 (plus I have access to an old Luger .22 for that). I'm not a big handgun expert, so the 9mm comment may have been out of line, but everything I read seems to point to the .40 and .45s getting the nod for defense purposes.