While I appreciate the in-depth reply, I already have a car deck that I like. Currently I'm using an LOD out of my iphone into the AUX port of the car deck and am now looking to do the same setup with an Android device.
Everytime I've tried using a car stereo's DAC (which is what I'd have to do if I used a USB stick or connected the device to the car through USB), it was always sub-par. Maybe the DAC's in a luxury car are actually good but I found my iphone 4s' line-out to be superior to any car deck I've yet compared it to.
I'm not DanBa (obviously) but I'd recommend getting a real car audio receiver. You won't have to pick up the phone to manipulate the player, for one thing, and most receivers nowadays can use phones (iOS or Android) as music storage. Or a USB drive. Plus the signal out of USB-powered DAC, and one that isn't running of a computer sending out 5v, is probably too weak to overcome the noisefloor in some applications.
Better yet, if you're actually serious about serious sound in your car, there are a lot of features on a real car audio receiver, and the serious ones are virtually the equivalent of a home theater receiver's processing power even if you're running stereo. For starters, you can use its active crossover to distribute the signal to each tweeter, midwoofer, and the sub, and thereby allowing you to use its Time Alignment processor to get the sound from each of these arrive at your ears at the same time. You can be sitting off to the left (or right if you're British in any way, including through colonization) but if you get the settings and installation right you can put the main vocals dead center on the dashboard with the other instruments spread out as they would be on a typical Hi-Fi set-up at home.