The court room scene in Measure of a Man when Picard turns around to the viewer "do you?"
https://www.youtube.com/watch?v=ol2WP0hc0NY
The scene with Guinan in that episode was also quite important
https://www.youtube.com/watch?v=-T9TUeapBSQ
The black and white vs. white and black faces in the TOS episode "Let That Be Your Last Battlefield" were quite brillant too.