After getting tired of my iPhone 3G sliding all over my passenger car seat I started shopping around for a car kit that would do 3 things I wanted:
1. Hold the iPhone in a visible location so I quickly see w/out having to take my eyes off the road for a long period of time.
2. Charge the iPhone while playing.
3. Play music through my Auxilary input w/out having to put the iphone in airplane mode.
I found a winner in the Kensington Liquid AUX deluxe car kit. I ordered mine through Amazon.com but it's also available at the Apple store and other places. It's a bit pricey but for all it does for me it was money well spent. Holds my iPhone 3G in place, charges, easily adjustable, plays music while not losing the phone option in case I get a phone call & even comes with a steering wheel mount remote so I wouldn't have to reach over and touch the screen to change music!
For those looking for similar options, you won't be dissapointed with this product. I've tried a Griffen kit but it failed miserably & broke within a week.
Apple Store (U.S.) - Kensington LiquidAUX Deluxe for iPhone and iPod