There are many very good websites that provide a wealth of information on GPS, these are just a few.

If you really get interested in GPS you may want to join the Institute of Navigation (ION)

There is even a magazine devoted to the subject of GPS called "GPS World"

Link to Zarlink for chipset specs                

Link to Dan Doberstein's company that offers a single channel hardware GPS receiver

Link to the university of Colorado

Link to NavTech which sells GPS related books and GPS receivers

Link to the US Coast Guard for GPS related information

Link to Sam Wormley's GPS page

Link to Peter Bennett's GPS page

A link to my friends at the GPS JPO

A link to the proposed European GNSS Galileo

A link to our Russian friend's GLONASS system

Link to SNAP - Satellite Navigation and Positioning Group at UNSW

Doug Baker's company GPS Creations for GPS hardware for running OpenSourceGPS