You want to knock out the grid, I'm thinking. That looks like some good info jancpb's got.

I just wanted to add the idea that there is a specific kind of bomb that knocks out electronics and nothing else. I don't actually know anything about it, really, other than it's called an electromagnetic pulse.

They used one in Ocean's Eleven... and a big one was the cause of the semi post-apocalyptic environment in the show Dark Angel.