45 ACP and 10mm are two of my favorite cartridges. Either would make a great personal defense weapon.
The biggest thing to remember in concealed carry is that smaller and lighter is better. A bulky or heavy gun will likely become a nuisance and be left at home before too long, which won't do you any good when you need it. No to worry, though, as there are plenty of small guns in these calibers.
I personally have a Glock 36 for my carry gun. Its thinner than any other Glock, being a single stack, light weight at 26 oz, and holds 6+1 of 45 ACP.