'Amityville 3-D' and 'Jaws 3-D' instantly spring to mind (for some strange reason) as third 3D movies.
Anyway, whilst bored and out of my mind at work I was thinking, what if it was the law to shoot every third film in 3D. Any genre, any time period just as long as it's the third film the law would apply.
Just imagine it...
Godfather Part III : In 3D!
That's about as far as I got with the idea but go and think about it for yourselves, it could have been pretty awesome!