Hi,
I bought a FoneM8 one from Amazon last week.
This being:
FoneM8 - HTC Desire PREMIUM Dedicated Windscreen Mount: Amazon.co.uk: Electronics & Photo
Seems good so far. Very solid and strong suction. Came next day as well.
I know it's a bit pricer than other kits, but it is specifically for the Desire and I wanted one that was seemingly well built and wouldn't fall of the window.
I haven't tried the car charger whilst using navigation but intend to test that tomorrow to see if the phone can maintain it's charge whilst using GPS as I know this can be an issue with some chargers.