La Haine: stunning depiction of bario life, and contains one my favorite musical moments in film (the estate DJ plays a mix of KRS One "Sound a' da' Police" and Edith Piaf "je n'regrete rien," I've used it as my ringtone for years).
Recent challenger:
The Orphanage (Le Orfanata)
I only watched this for the first time earlier this week, it's still giving me chills whenever I talk about it to people.