8mm Mauser. I am considering this rifle at the moment, as it is cheap to own, cheap to shoot ($.07 per round, but corrosively primed) and it very good quality.
Like others have said, heed the "dont buy until you know what its going to be used for" advice. If you buy a .22 you wont be able to go hunting for anything but small game and self-defense will not be a viable option. However, if you buy a 700 Nitro Express, you wont be able to hunt anything on this continent without having to package the instant hamburger you just made.
A lever action in a pistol caliber is a good choice, as ammo is plentiful and it can be used for hunting and SD in a pinch.