Directed Electronic has a neat little gadget for your car: SmartStart. SmartStart RemoteStart will let you lock your car and arm the alarm, as well as unlock and disarm the the alarm, open the trunk, trigger panic mode/car finder, and even let you remotely start your car and pre-heat/cool the cabin.
It’s not cheap though. The complete kit will cost you US$500 plus US$30 per year after the first year. The app, which is available for Android, iPhone, and Blackberry, should’t cost you anything from their respective markets or app stores.