MONSTER AI 300 FM-CH iPhone(R)/iPod(R) iCarPlay(R) Portable 300 FM Transmitter (123898)
Like that it can play without a wire (pass to the back seat to pick songs.  The negative is that it doesn't insert into the iPhone 4 while in it's OtterBox case (a problem with other plug stands and players).  Limited use as a consequence to date.