Easy:
-City of God: Brazil drug life
-A Beautiful Mind: One of my favorites; Nash Theory.
-Godfather (1 & 2): To omit Vito is to omit opulence; can't do that.
-Scarface: Tony Montana; nuff said.
-Training Day: Arguably one of Denzel's finest roles (but I concede there are others in his collection that are a worthy replacement).
-Schindler's List: Just watch.
-Ocean's 11: The boys took the bank!
-The Excorcist: Still one of the benchmarks for scary movies/horror.
-Wall Street: Every investment banker of the last 20 years will list this as an inspiration; certainly was for me.
-Anchorman: The most quotable, laughable, all-around brilliant movie Will Ferrell has ever done. He's been steady falling since...
R
**Edit**: Special mention to Asian cinematography (so good!): House of Flying Daggers, Hero, Memoirs of a Geisha, Crouching Tiger Hidden Dragon, etc etc.)