How about using the low cost, highly effective method of being smart about parking your car??? I know this may not always work, but you'd be amazed at how often a car is stolen from a spot that wasn't safe. Back of the parkinglot, dark corners, topmost floors on parking garages, alley's.
Use some sense. If you're still paranoid, I'll sell you a Clifford Avantguard 5 with wireless immobilizers, a pain generator and more sensors than Air Force 1, then add a GPS tracking system with a theft protection guarantee and you're set with the best security system on the market that cost 3 times the amount of your insurance deductible.