Courtesey of my favorite blog of the moment, Boing Boing, is a pointer to a Popular Mechanics article that outlines an extremely scary future terrorist scenario.
Short version: for very little money — as low as $400 — it is theoretically possible to construct a device that would set off an electromagnetic pulse capable of destroying pretty much all electronic devices in the immediate vicinity (unfortunately the Popular Mechanics folks forget to include how large of an area such a device could effect).