Helicopters are great as a photography platform, it is possible to get an exceptional view.
Try to get the pilot to fly with the doors off, as it will allow you to photography without looking through windows and gives a far better view. Photograping through the windows will give great loss of contrast in the images.
Lenses between 20mm and 100mm will prove to be the best focal length range, use as fast a shutter speed as you can, to avoid any camera shake or vibration from the helicopter. Lenses with built in vibration reduction or image stabilization will be a great advantage.
