ALK Technologies adapted its GPS app to Apple tablet computer, it is called CoPilot Live HD. In order to make it work and help you, the iPad 3G is needed, as the program works only on this device, and, of course, the application itself which will cost you $30.
However, it is worth it, as there is possibility of 2D and 3D maps simultaneous combination, voice functions, CoPilot Live HD works in portrait and landscape orientations.