GPS theft tracking

Anyone know of a good GPS theft tracking system that doesn't have to be professionally installed?

Crutchfield has this one but its service is fairly expensive:

http://www.crutchfield.com/S-kDYPeNgJdwb/cgi-bin/ProdView.asp?g=282850&I=667IQSILV

you have to keep paying on a regular basis for the service even if you don't use it.

I found these that seem cheaper in the long run:

http://www.mymobileguardian.com

http://www.omegagpstracker.com

but those two have to be installed by a shop that deals with them. If anyone is going to mess up the inside of my Z it's going to be me I just can't see turning the car over to them to install and wire it.

I'm not looking for any sort of continuous information from the car, some of them seem to be teenager watching systems. I don't need to know where it is except when it is stolen. And I don't need to be reminded of how fast I went.

Ideally I would never actually use the service because if I did it would mean that the car was stolen. Just somewhere to login or call if the car is gone.

-Trevor