We got one on the Clio, and it seems to be very comprehensive. It claims to provide the same level of cover as the original manufacturer's warranty. I've just dug the little leaflet out, so here goes:
Items covered: Engine, gearbox, driveshaft, casings,
seals and gaskets, water pump & thermostat, starter motor, alternator, wiper motors, radiator, steering rack, electronic ignition, fuel injection, heater motors, wheel bearings, central locking, clutch, air bags, air conditioning, audio equipment, braking system/ABS, cables, catalytic converter, computers, gauges, hoses, satellite navigation, suspension, turbocharger, wheel hubs
Items specifically excluded: Routine service & maintenance, bodywork, paintwork, trim, glass, normal wear & tear, exhaust pipes, batteries, tyres & wheels.
There's a more detailed document but I can't find it right now. It listed the exclusions and they all seemed pretty sensible things that would fall under the 'normal wear and tear' category (bulbs, brake pads, fuses etc.) We've just had a faulty indicator switch replaced free of charge under the warranty, so electrical bits certainly seem to be covered.