Does it die and then not restart? I had a funny problem a while back where the car would just die, it turned out it was just a loose key cylinder and heavy key chain. It took me forever to figure it out because the car would obviously fire right back up, easily, as there was really nothing wrong with it. It would just baaaarely slip into the "off" position. The solution was just to put my janitor-size key chain on a diet.
TFI module (flat thing on the side of the distributor) is probably the most common problem to cause this. That said, all of the above comments are true as well, plus many other things as well.
I had a 95 GTS that was doing that. Turned out to be the ignition module inside the dizzy. I figured it out by pulling up a 94 vert beside it and started swapping parts until i figured out what stopped it.