Mustek PD77
Price: £139 Screen size: 7 inches
Clever twist on the dual-screen idea. One of the screens is a tablet-style player which, in theory, makes it easily usable on its own away from the car. The only snag with this approach is that the unit doesn't have a battery, so you'd need to be close to an external power source to use it. The screens are sharp enough when viewed from straight ahead, but lose clarity if you're watching at an angle.