Maria's first appearance in the pleasure gardens, surrounded by ragged worker children; "Look! These are your brothers!" And, for some people, the ending.
In the novel, Rotwang's death: while hanging off the edge of the cathedral, he hallucinates that Hel is reaching down to embrace him, and he lets go so he can touch her face. Also, Joh Fredersen's redemption epilogue where he's given a letter Hel wrote before she died saying that she'll always love him and that she knows he'll rediscover the goodness in his heart.
In the movie, when Freder finally meets Maria face to face, as well as the preceding few minutes especially with the music attached.