I don't know if all airlines have them, but Air Lanka and Emirates do.
As well as the normal movies, games and entertainment channels on the seat displays they have also external camera views showing the view ahead and the view directly down from the aircraft.
You can watch the landing and the picture is superb. Whilst cruising you can also look directly down at the passing terrain.
the down view isn't so interesting, but the ahead view during take off and landing is quite spectacular. The front view camera must be mounted near the nose wheel as it clearly shows the vehicle pushing the aircraft back prior to taxiing.
But the cameras are on for the complete flight, so they are external cameras.