I went for the Griffin 'RoadTrip'. It took a while to find a supplier that actually had them in stock, but I now use it in the car and find the results pretty good.
I have the charcoal one, which goes well with my black 30GB iPOD Video.
Essentially it is a docking cradle which plugs directly into the ciggy lighter (comes with adoptor and extension arm). The FM transmitter is powered from the 12v supply and the range of frequencies gives plenty of choice. I currently use 107.9 and get virtually no interferance.
http://www.ithings.co.uk/item--Roadt...tripblack.html