Here comes the Eclipse AVN2210p by Yaris SR in Europe, which includes a detachable TomTom portable navigation system.
For this setup, you can use the 3.5″ touch screen as an interface for the car stereo and when docked into its place the TomTom charges its battery so you never have to worry about unsightly cables and such.

It’s a double-DIN sized audio unit that has a USB port, bluetooth, offers satellite radio capability, and with an extra attachment it lets you control your iPod too.

You can pick one up here in the US. Eclipse AVN2210p currently costs $500 on Amazon (or $600 if you want the blue backlight). AVN2210p maybe the solution for those Prius owners who are going mad because they can’t control the GPS navigation system while driving.