Okay, it may sounds basics for French people, but it is quite impossible to write several articles about Saint Denis without writing one about French Hip-Hop band NTM. If you don't know them, I would say they sound a bit like Public Enemy in US and are still considered nowadays as the louddest voice of Paris' northern suburbs. Fifteen years after, problems are exactly the same and no other solution is considered that increasing repression...There are some very big urbanism issues there, but it seems that there is no will from any state to work on it.
Best movie you would probably watch about this issue may be Matthieu Kassowitz's La Haine (1995)
1993: 1993, j'appuie sur la gachette (1993, I pull the trigger)
1995: Paris sous les bombes (Paris under attack)
1998: Suprême NTM