Daymo said:
Gran Torino for one because it was just a fantastic film over all and Scott Pilgrim because all the flash and sound would be greatly improved in the cinemas. The battle with the twin ex's would be just so much more satisfiying.
I did see Gran Torino in an almost empty Theater (I think there was something like 8 people in it), and it was certainly wonderful. I even stayed through the credits.
But on Scott Pilgrim, I agree. I never got to see it in a theater, but I so would have if the opportunity had been available. The closest replication of it was at home, on my big screen and surround sound, but budget surround sound, not Bose stereos or anything.
OT:
A Nightmare on Elm Street (1984). The first 20- 25 minutes in a packed house would have probably been intense.
The Exorcist - Just to have seen people freak out over it when it first released.
Enter The Void - I heard it was also in 3D, so to have seen it in 3D and on a Big screen... That would have been intense.
Hausu - Because why the hell not?
Fritz Lang's Metropolis - I can only assume how cool it would have been to have seen the complete movie before it got cut to hell.
That's all I have to say about that.