I installed a built in garage door remote control in my car over the weekend.
I picked up a Skylink remote for $22 at the local Home Depot. It can operate pretty much any garage door out there, and it uses a 12 volt battery.
Wiring was straight foward. I used the 12 volt power source from the glovebox flashlight charger to power the remote. I wired in a non-lighted power window button to the button on the remote, and installed it in the factory fader location.
It took me about an hour to install and it works great!