Receiving GPS signals itself is free.
The program you use to read the signals and provide navigation might not be.
GPSTest for instance tells you where you are (longitude and latitude). Not very useful in itself. Google Maps is free, and puts a GTA2 like map with a Dot on it where you are.
TomTom puts a GTA3 like map with direction based navigation (but isn't free).
Some not free applications:
- TomTom (once off charge for maps)
- Wayfinder (one charge for limited period of use i.e. 3 years)
Hope that helps!
By the way, consumer GPS devices are [hard] coded to recieve updates only 1 or 2 times per second, hence they are inaccurate to about 10-15 meters. Rumour is that US military recievers are coded to recieve several (10+) updates per second, and therefore are far more accurate (you wouldn't want to bomb the school next door with a missile fired from 100km away now would ya