I spent quite a long time researching this for my 2002 focus. In the end I found the best solution (though by no means the cheapest) was by Brodit
http://www.brodit.com/
I plumped for the 915246 Holder with Pass-Through Connector. The dock is very solid, and is felt-lined so it doesn't scratch the iphone. You attach it to your vehicle's dash using the relevant pro-clip also available from brodit.
It also means that all you have to do is plug in an iphone dock cable into the bottom of the holder (no unplugging and re-plugging when getting in and out of the car)
I went for the Griffin PowerJolt SE cigarette lighter charger, which I got my local ICE dealer to install behind the dash, and to run the cable through a small hole in the fascia. This means I can use the cigarette lighter for charging other devices.
I also have the Alpine iDA-X001 head unit which can control ipod/iphone through the head unit. This has a dock connector, which again I can plug into the bottom of the cradle if I choose. I don't do this for 3 reasons.
1. My iPhone is 16GB and doesnt hold all my music, my iPod is 80GB and does.
2. Whilst the iPhone does work with the Alpine unit, I get an annoying compatability message eveytime I plug it in.
3. When switching between data networks, or when using the GPS in maps, it causes static in the music stream to the head unit. Much like that generated when leaving a mobile phone next to computer speakers and a sms comes in.
Below are pics of my setup. The dock tilts and swivels 360 degrees. The ipod is shown in the dash pocket, and the cable from the alpine unit comes through the back there, slack can be pulled through for connecting to the iPhone if needed. And yes I know the iPhone is covered in fingerprints, i didn't realise how dirty it was until the flash picked it all up.
http://i66.photobucket.com/albums/h244/chrisgazzard/CIMG6830.jpg