I recently watched Magnolia in the Prince Charles Cinema in London. I'd seen it multiple times before, but never in a cinema. The bit with the frogs was incredible, going from peaceful to absolutely deafening. That scene is now my most memorable.
There are so many movies I haven't had a chance to watch in a cinema, I wish more theaters would play classics on their largest screens. I just found out that one of our local cinemas now has weekly 'classic sneaks'. Lucky me.