It's more than likely the ignition switch. It's a pretty common problem. When the car shuts off, does the green security key on the dash flash? When it shuts down, do you lose the gauge lights but the radio still works? If so, it's definitely the ignition switch.
Oh and I have an ignition switch if you're interested. I'm in Jersey if you want to buy it. Free install if you come to me. Reason I have an extra is I had the same problem. Turned out my problem was my aftermarket alarm being flaky.