I was looking for a car-mount solution for my iPhone and I found a solution that works well for me. Maybe it will work for you as well.
I wanted something that required no permanent changes to my car, so I bought the Panavise BMW Z3 Cell Phone & Media Mount. Basically, it's a metal bracket that wedges itself between the passenger glove box area and the center air vents. The good thing is that it's removable (with some work) and you would never know it was installed in the first place. I combined that with the ProClip USA iPhone padded holder with tilt swivel. It's really a pretty good holder - it swivels in all directions (important for a roadster since sun glare can be bad) and it attaches easily to the Panavise bracket with just four screws & nuts.
Next, I needed to actually attach it to my car. Using the AUX-in audio for my radio and a charging solution I discuss in detail here, I was able to get the phone charged and get audio out.
One final thing - a small bit of velcro attached to the back of the dock connector and the back of the Panavise give me somewhere to attach the iPhone cable whenever it's not in use.