NaviBoard
Forum specifically on the topic of GPS (devices, software etc.)
GpsPaSsion
Lively forum around GPS HW & SW.
Laptop GPS World
Forum specifically on laptop GPS
Geosoft
Introductory GPS info by Michal Schulz in the PowerPoint-style.
Kowoma
Extensive information on GPS and Geodesy.
GPS-Infoseite von Ralf Schönfeld
Lots of information and practical tips around the topic of GPS