iPod shuffle: Free (mail-in gift with purchase)
DLO Transpod Wireless Transmitter: $19 (on eBay)
Being able to easily take a nice variety of music with me when I drive: PRICELESS!I'm spoiled. I've got an iTrip for my iPod, but unless I'm going on a long road trip it's not worth the hassle of packing all the crap (power adaptor and cup holder adaptor) and dragging it with me. Now that I've snagged a bargain on the nicely designed compact DLO unit, it's easy to grab it and always have a good selection of tunes in the car. Hardly "CD quality" sound, but as good as a clear radio station.
Increasingly, car manufacturers are making iPod friendly interfaces available. Until we get new cars that include that feature, I'll get by using the current method. For a good overview of the pros and cons of all the options:
6 Ways to Link iPods and Car Radios.