This little device from AvaTrac combines GPS and a quad band GSM modem to ensure that you never lose your car again.  The device gives you a ton of security options, like remote vehicle tracking and remote engine kill.  You can even connect a panic button to the AVL802 to send out an alert if you are ever kidnapped.

It seems like this is a good solution for commercial vehicle fleets, or parents worried about teenage drivers.  No word on pricing, but the use of a GSM modem probably means this thing will come with a subscription plan.