Doggie GPS- Global Pet Finder and the Garmin Astro

The Global Pet Finder is a GPS dog collar that your pooch wears at all times. It has a unique ID that constantly monitors your dog's whereabouts. You log into the Global Petfinder website and a map pops up showing where your dog is currently located.
The Global Pet Finder can also send a text message to your cell phone if the dog leaves the perimeter of your yard. 

One caveat — if the dog is out of cell phone range, his location can not be transmitted or tracked. An alternative solution for areas without cell phone service is the Garmin Astro dog tracker. It's a much more cumbersome device that the dog wears strapped to its back. But the Astro uses its own radio signal to transmit the location of the dog to the handheld GPS receiver that the owner carries. If the dog is within five miles of the owner, the receiver uses a compass interface to point the owner to the dog. This solution is best suited to hunting or camping with your dog.

http://www.globalpetfinder.com/

http://www8.garmin.com/astro/