UPDATED LIST. #'s 1-5 are all four star films.

1) Taxi Driver
2) Raging Bull
3) Mean Streets
4) Goodfellas
5) Casino
6) The Last Waltz
7) The Aviator
8) Cape Fear
9) Gangs of New York
10) Bringing Out the Dead
11) Boxcar Bertha

While Goodfellas is a masterpiece of style, the top three: Taxi Driver, Raging Bull, and Mean Streets are all films I can never stop thinking about when I see them. They are among the best films art-wise, especially Taxi Driver, which is definitely one of greatest character studies (if not the best).