As always, I recommend a .45 for personal/home defense, its what I carry. We still use .38 specials at work, and I've fired both the 10mm and the S&W .40 a lot, but I still think the good old .45 ACP is the best you can get. It almost guarantees to knock down or stop with the first round, and its low enough velocity that if you use soft or hollow points theres very little chance of the round passing through and continuing on to hit someone else. Plus that big gaping hole staring at someone has a great intimidation factor that can't be overstated for self defense- people are scared of a .45, much more so than a 9mm.
I carry a Colt MkIV, basically identical to an issue M1911A1, but with better sights. I use Winchester hollow points for carry, but normal FMJs for target shooting.
And whatever calibre you settle on, I'd suggest looking into specialised Home Defense ammo (brandnames are eluding me at the moment), they're designed to break up on entering a person or passing through a wall to minimise the chance of the bullet either missing and hitting someone outside (or in the next room) or passing through the target and hitting someone else.