There are quite a lot of options. I have a Dell X5 running Tom Tom Navigator 5 from an SD card which I've found to be extremely good so far. At the moment I use a wired GPS receiver which shares the same cigar lighter power lead in the car. My PDA is not Blutooth but I think I might add a Blue tooth CF card and upgrade to a bluetooth reciever to save the wiry mess. Tom Tom is one of the more popular products, but I think it's a matter of personal preference. You load the software on your PC and transfer it to your SD card from there. Also check out click here
herc 182 - you mention using it as a tracking device (?)- I use Ipaq 3870 with Globalsat BT308 Bluetooth GPS and Tom Tom Nav 5 which is excellent for voice guided navigation - Tom Tom Nav 5 will also record your journey if that's what you want to do.
Suppose it is a little pricey but shop around and you can get the bluetooth and tom tom 5 for £150. You can always get a cheaper mount, but i find that if the t3 isnt plugged in to charge it auto swithces off. The benifit imho is that you are only carrying one piece of kit around. I would never leave a gps in the car and when i go, the t3 just drops in my bag.