XtremeMac have just announced the AirPlay FM transmitter for the iPod - looks like an excellent rival to the iTrip: no installation of playlists needed and doesn't cover the hold switch, both of which are annoying features of the iTrip, and the same model fits iPods and minis.
(I am not affiliated with XtremeMac in any way...)
(I am not affiliated with XtremeMac in any way...)