This is probably the best iPod gadget for your car, the 4-in-1 iPod car kit.

The iPod Car Kit includes a cradle to hold the ipod, a charger that’s powered off you cars cigarette lighter, an FM Transmitter so that you can listen to your iPod over the car stereo and a remote control so even rear seat passengers can skip tunes (though if you have kids that class the Crazy Frog as music you may not want to tell them about the remote :))

You can get the 4-in-1 iPod Car kit for $28 from Brando, which is a bit of a bargain IMO.