IMO....If the vertical distance from the top of the shower threshold to the lowest part of the light fixture is more than 8'-0" you can generally [excluding track lighting.. IMO (410.101(C)(3)] use any type fixture than you want [410.4(D)] 2005NEC.
If the distance is less than 8'-0" you must use a fixture rated (by the manufacturer) for damp locations. Most recessed cans that I use meet this requirement if you use a shower trim.
If there is a chance that the fixture will be subject to shower spray you should use a fixture rated (by the manufacturer) for wet location.
If the walls of the shower stall go all the way to the ceiling, I would use a fixture rated for wet location regardless the distance.
GFI protection is not necessary unless required by the manufacturer.
I always use a fixture rated for damp locations (at least) regardless of the height if it's above the shower (ever took a hot shower in a cold bathroom?)
The NEC is a minimum. A good installation may require more.
just my 2 cents.
steve