Pioneer's AppRadio 2.
If you own an iPhone, you can choose from a surging sea of add-ons that work with it: speaker docks, in-car gizmos, game controllers, and much more. If you have an Android phone–well, if you’re lucky, the company that made it sells some peripheral devices. (Motorola, invented of such add-ons as the Lapdock, is especially conscientious here.)