I would suggest somthing blunt and heavy that can be used in tight spaces. most homes will have halways and such that will make swinging a full sized baseball bat cumbersome. Get a couple of aluminum kids tee-ball bats. Short, light, but it will hurt like heck when you hit them over the head. Another pretty easy thing to do is get a heavy duty tubesock(ones for hunting work well) Keep your spare change in it. Great little beater if you can get a about ten dollars in there in small coins. Tie a knot in it so all the coin is gathered at the bottom. make sure you have enough cloth left to swing it well. You can do a lot of damage with this in a small area just practicing hitting with wrist motions only.
Best bet though against any intruder, is a good sized Dog if you can get one. It doesn't really have to be a mean one, like a pitbull, but mean looking will help. Rotties are great for this. Very protective dogs, with a good size and a great bark. Get that AND the small baseball bat.