I use Pandora all the time in the car with the DLO TransDock. It's an iPod FM broadcaster that has an aux in (which I use for the iPhone). It doesn't charge the iPhone, but that's why I have an external battery.

Motorola has a bluetooth adapter with a built in FM transmitter that supposedly works very well. The iPhone currently doesn't support A2DP (stereo bluetooth), so it doesn't work right now, but the 3.0 update will make it compatible. A dash mount, a plugin charger and the Bluetooth FM transmitter should make for a servicable setup with a stock radio.