Hi, I've used several transmitters and have not been happy with any but the one linked below. Most i have tried produce a poor quality should, or interference from the engine can be heard. This transmitter can overpower radio 1 so your ipod can be heard over the frequency radio 1 uses. Good news for people like me who travel round the country and don't want to keep rescanning for a new FM frequency.
Its downside is the ipod does not plug into it, you have to use the provided phono (3.5mm) to phono cable. This does mean you can use and device with phono out, but it wont charge your ipod.
link:
http://www.supermediastore.com/insten-appl...ar-charger.html
I purchased this item from UK but cant remember where from, but this is the same item.