I have used the sparkfun module (LS30001) it is very accurate. Down to about 6". There is a library called TinyGPS. that will get and parse the values into an object so you can use them within your sketch. I have an example sketch that uses this library to find the distance between two points on earth using the harversine formula.
can be found here: http://apexlogic.net/code-bank/arduino/serial-gps-find-distance-between-two-points/
it has links to the TinyGPS as well as the actual module datasheet. Enjoy.