Get an iPod/iPhone FM transmitter for free (after rebate)
An FM transmitter is often the best (or only) solution for listening to your iPod/iPhone tunes in the car. This one's free after rebate.
If you want to listen to your iPod or iPhone in your car, you have precious few options. You can spring for a pricey stereo dock that requires pricey installation. You can use one of those tape-deck adapters, assuming your car is old enough to have a tape deck. Or, you can try an FM transmitter, which broadcasts audio from your player to an unused band on your stereo. Buy.com has such a product, the aptly named Av Lab iPod/iPhone FM Transmitter, for free after a mail-in rebate [PDF].
Compatible with most iPod and iPhone models, the transmitter features a backlit LCD and plus/minus buttons for setting its broadcast frequency (anywhere from 87.9 to 107.9). Find an unused frequency on your stereo, set the transmitter accordingly, and presto: your music should come piping through your speakers.
Full disclosure: In my experience, FM transmitters generally suck. But your mileage may vary. And, hey, it's a freebie! After you pay your $14.99 (shipping is free), you get back a check for $15. So you actually pocket a penny. Heck, it's like you're getting paid to buy this! (I know, I know, the stamp...)