Been waiting for Griffin's car mount for the iPhone 4. The WindowSeat I used for my 3GS was great.
Make sure to use GRIPHONE4 coupon code on checkout for 20% off + free shipping.
WindowSeat AUX:
http://www.griffintechnology.com/products/windowseat-aux#
WindowSeat HandsFree, the same as above but adds a microphone to the AUX cable:
http://www.griffintechnology.com/products/windowseat-handsfree#
Make sure to use GRIPHONE4 coupon code on checkout for 20% off + free shipping.
WindowSeat AUX:
http://www.griffintechnology.com/products/windowseat-aux#
WindowSeat HandsFree, the same as above but adds a microphone to the AUX cable:
http://www.griffintechnology.com/products/windowseat-handsfree#