A GPS receiver is what allows you to determine your position using FlightMaster. The market is literally full of so many different makes of GPS receivers. Virtually any of these will work with FlightMaster, so it's not difficult to choose one.
The important consideration is NMEA-0183 compliance - as we said, virtually every GPS receiver on the market today supports this standard.
We recommend you get a Bluetooth receiver (e.g. a Holux M-1000, pictured right). Bluetooth is a wireless technology which allows you to connect your PDA to other devices (all the PDAs mentioned on the previous page are equipped with Bluetooth).
In the cockpit, this translates to less cabling. The downside is that your PDA will use slightly more power, but you should still get 2-4 hours usage.
Most Bluetooth GPS receivers are capable of 15-20 hours of continuous operation from a single charge, so for most flights you wouldn't need to have the GPS receiver plugged into a power source - saving one more cable.
You will also need an SD card, with at least 80MB free space on it. The SD card holds the terrain databases, which are too large to fit comfortably in most PDAs.