I used the iriver for a long time. Its differant from most FM tuners in that it plugs directly into your cigerette lighter adapter. I don't know if conducts the FM signal through the car or what....but I've used the cheap FM tuners right up through the expensive Belkins and the Iriver has far surpassed the quality of all of them in my opinion. Since it just plugs into the ligheter adapter, it's use is best suited for automobiles.
http://www.gizmodo.com/gadgets/porta...ter-025443.php
EDIT: I just realized the link i provided gave this unit a horrible review!! =P