IMHO you really get what you pay for when you buy one of these FM transmitters. I have wasted money on several brands before asking a teenager what she used. The brand I have found works best is DLO. They make a holder that plugs into the lighter and keeps the iPod accessable and also a more compact unit that also plugs into the lighter, but then attaches to the iPod via a 24" cord. The good thing about both units is that the iPod charges when connected, the bad thing is that I can't charge my phone nor my Garmin while listening to music.
I rarely have any static problems or interferance any more since I tuned the xmitter to 107.9, the highest freq available on FM. When there is a problem it is easy to jump 1 channel higher to 87.9, the lowest channel on the FM band. The DLO rolls over to the start automatically when manually tuning. We have used this all over the US as well as France and Italy, no more europop for vacation soundtrack!!