I've done a bunch of homework on this, and after agonizing over which one, I came up with this one, and have been incredibly happy with it:
Amazon.com: Arkon Universal Windshield with Dashboard and Vent Mount for Smartphones and PDAs (Black): Cell Phones & Accessories
Akron SM310
I bought one that works for both the windshield and the vent. My reasoning was if I switch between cars, I may need the windshield mount if I want something that works. The arm on the windshield one looks pretty thin in the picture, but that is one sturdy mount. It has a big suction cup on it with a lever that pull a lot of vacuum. Vent mounts are all pretty much alike. The holding assembly is made so it doesn't interfere with any part of the phone that would get in the way of its operation. There is cut-outs on the side so you can easily get at the volume rockers, and on the bottom, the fingers are out of the way of both the USB and 3.5 mm headset. Because it grips from the side, it doesn't matter if you decide to get a larger battery or protective case later. In fact I did get a protective case. Putting it in is a 1 second operation. You drop it on the little feet and squeeze the sides together. To get it out, you slide the little lever and the sides snap open. This mount is a dead-ringer for a Touch Pro2.