Some other great ones i haven't seen posted yet.

Michael looking Kay dead straight in the eye and saying 'No' at the end of GF I.

Michael's eyes just before he shoots Solozzo and McCluskey in the restaurant.

Michael's thunderstruck look when he sees Apollonia for the first time.

Vito's face after Tom tells him abt Sonny's death.

Michael's 'gangster walk' right after Carlo is killed in the car. His face is so expression-less but cold in that scene. His defining moment in GF I.