I sold my old iPhone and got a Droid with car dock from Motorola. Google Maps Navigation on the Droid is well designed. The car dock is not.
The dock holds your phone - and that's it. If you want power, you need your own usb car charger. If you want audio from the phone to the car stereo, you need another cable. One nice feature though, is that it allows for easy rotation of the phone between landscape (useful for navigation / watching YouTube videos) and portrait (useful for calling people / web browsing) orientations.