This thing's probably not legal in the UK, or many states in the US, like California, but Polaroid has combined a GPS Nav system with a DVD Player.
The navigation itself isn't anything out of the ordinary. It uses the Sirf Star III GPS Processor and has a touchscreen interface. But, the 5.6" screen allows you to watch The Fast and The Furious while you're barreling down the 101 at 5 miles an hour.
Also, the system has a built-in FM transmitter, so that means you can listen to the audio from your movie through your car's speakers. However, you can't listen to music and this at the same time, unlike in-dash navigation systems.
Available at Target.
MGX-0550: Portable GPS with DVD Player [Polaroid via Digital Lifestyle Magazine]