Do your reasearch...becuase you should worry about the quality of the Transmitter. Depending on where you are, the FM transmitters work at varying qualities.
Griffin's iTrip 2 is supposed to be alright, and work in areas of varying consistency. But it leechs battery life off the iPod if i remeber correctly.
Belkin has like 3 different FM transmitters, and they work depending on where you are. It works well in some places and not so well in others. You can use these in differerent players other than the iPod.