For quite nice car stereo integration http://www.gromaudio.com/ offers pretty nice post install boxes for quite a range of car models. Offers bluetooth streaming & usb harddrives & aux & android phone clients.

I've installed one box in my Volvo and it integrates quite nicely to volume and next/previous buttons on the car wheel. So I can control my ssd drive which on glove compartment from my wheel.

Not directly releated to car holder as such. Just mentioned if someone would be interested post-install systems on their cars.