Great thread. I'd love the idea, if some other users would also start a thread on their 25 favorites 
When I first watched Mirror at the cinema, I wasn't overwhelmed (though I was already a Tarkovski enthusiast). Since then, the film has grown in my memory and become one of my favorites. The first scenes of the film, with the protagonist sitting outside of the house and waiting, are one of the most marvelous transferences of nature onto film. 
Nykvists cinematography in Offret (1986) is also remarkable. I'd say that Angelopoulos was inspired by this in his later films.

Rear Window is by far the most complex film by Alfred Hitchcock I have seen so far (out of 25 movies). The last time I saw it on a large screen I was astounded by the many layers present in the film. The plot and ongoings were secondary as I was exploring the philosophical questions inherent in the material. But I must say that I like some other films by Hitch much more. 

Keep the comments coming Mik!