GSI Super Quality Mini FM Transmitter/Modulator + Car Charger Cigarette Lighter Port Kit + Full Function Remote Control - LCD Display, For Apple iPhone 3G/3GS/4G, iPod Nano, Touch, Video, Classic
This device allows me to listen to podcasts and music stored on my iPhone 3Gs through my car's speakers by transmitting an FM signal that the car radio picks up.  It's small and easy to use, and the price was amazingly low.  The only problem I had was finding a frequency that was free of static.  At the low frequency end, say 89.5 MHz, it sounded OK until I started driving, when static became a problem.  I found a high frequency, 104.5 MHz, that was reasonably free of static, though I had to experiment with