I borrowed this holder (Nokia 5800 CR-119 Car Holder) from a friend of mine before buying it myself. It was perfect, the holder didn't shake whilst the car was moving; unlike other unofficial holders I have used in the past. It also allows you to have the phone horizontally OR vertically depending on your preference I suppose.
The only thing I would say you should look out for is when you turn the holder to change the phones orientation be careful, as if you turn in the wrong direction you'll unclip the holder from the screen mount.
Overall a perfectly designed product, what more could you ask for?