The Gumstix Verdex comes with a GPS Expansion board which carries a uBlox GPS module spitting out data in NMEA format. It also has power supply for an active GPS antenna and I got a simple one to test things out with.
The GPS will need to be supplemented with assistance from CORS stations, IMU and possibly ultrasonic or laser range finders on board the flying UAV platform. We can try out a newer ublox with online almanac update features, but I doubt that performance will be much better.
Together with GPS the other power consuming part of a UAV system is the control radio. Thanks to the emerging Zigbee radios we can do with very low power receivers and great range from the XTend modules (advertised at 40miles). With these we can obtain near real-time high level control interfaces and synthetically coded channels.