I custom made an iPhone dock with USB charging, aux-out through the dock, and it even charges my bluetooth headset, all in one plug. I custom-made the mount itself because every other car-mount I've seen is too large and bulky. This one is tiny and unobtrusive.

I made it by taking a portion of the packaging that the iPhone 3G ships in... There is a small plastic tray in the box that holds the phone itself. I cut a portion out of that tray and heated up the sides with a candle and curved them around so that they cradle the sides of the phone. (When I upgraded to an iPhone 4 later, I did a little more work to the cradle to make it fit that phone.)

I attached all of that to a custom-modified Apple iPhone Bluetooth Headset Charger plug. The modifications allow aux-out to work on the plug, which is running to the aux-in on the 'peg. Inside the dash, it connects to a 12-volt aftermarket USB charger. Details of this modification (and some problems I had with it after the IOS 5 upgrade, mostly solved now) are in another thread here on the BBS.

With a little help from my housemate, I made a custom metal bracket that mounts it to an existing screw on the instrument panel cowling.

The result:
The phone sits up perfectly straight, just behind the steering wheel. From my driving position, I can see the entire iPhone screen, and the top edge of the phone is just even with the bottom edge of the windshield. I've been using the TomTom GPS software for navigation, and this arrangement is absolutely ideal. I can also listen to Pandora thanks to my being grandfathered in to AT&T's unlimited data plan.

Still prefer listening to the 'peg, though.