All other films are foreign, and thus immediately suspect. (I kid, I kid...) But as great as movies like A Better Tomorrow and Eastern Promises are, I have a hard time seeing them as gangster movies in the way that The Godfather is a gangster movie. Gangster movies are, I think, among the most American of film genres, and I'd like to keep the following list as "American" as possible.
This said, and in no particular order, I present:
1. The Godfather I and II (of course) (1972 and 1974)
Synopsis: Directed by Francis Ford Coppola, and featuring a cast of actors who would become household names, The Godfather Parts I and II tell the story of the Corleone family and their rise to power.
Despite the fact that I like some of the movies on this list more than either of The Godfather movies (don't bother with Part III), it has to be first on any list of gangster films. Why? Because the others simply wouldn't exist without it.*
Best Scene: Michael Corleone getting payback for the attempt on his father's life.
Six Degrees of Gangster: James Caan would go on to star in Thief, another great gangster movie. Al Pacino would star in Scarface and Heat, also listed below. Robert De Niro, who played Vito Corleone in The Godfather Part II, appeared in 5 out of the 10 movies on this list.
Fun Fact: The book by Mario Puzo is great, too. Around the same time Puzo wrote the script for the disaster film Earthquake! starring Charlton Heston.
2. Goodfellas (1990)
Synopsis: Directed by Martin Scorsese and starring Ray Liotta and Robert DeNiro, this movie focuses on the struggles of two half-castes within the Italian Mafia.
Best Scene: A lot of people would probably say it's Pesci's "What, do I amuse you?" moment, but I think the "shoeshine box" argument is even better. This movie is full of so many iconic scenes that it's hard to pick just one.
Six Degrees of Gangster: Joe Pesci would go on to star in Casino with Robert De Niro. Ray Liotta costarred with Sylvester Stallone and De Niro in Cop Land.
Fun Fact: Pesci's "What, do I amuse you?" scene was improvised, and was based on a confrontation he'd had with a real-life mobster years before.
3. The Departed (2006)
Synopsis: Directed by Martin Scorsese and starring Matt Damon and Leonardo DiCaprio, this might just be the greatest gangster movie of all time. In terms of sheer watchability, I'd put this story of Irish mobsters above even Goodfellas and The Godfather.
Best Scene: Wahlberg and Sheen interviewing DiCaprio for his undercover assignment.
Six Degrees of Gangster: Robert Wahlberg, brother of Mark, who appears in this movie as FBI agent Frank Lazio, has also appeared in several other gangster movies of his own. And speaking of Mark, he's also good in We Own the Night, which also features a great performance by Joaquin Phoenix.
Fun Fact:This movie started out as a remake of the Hong Kong gangster movie, Infernal Affairs.
4. American Gangster (2007)
Synopsis: Directed by Ridley Scott and starring Denzel Washington, this movie details the rise an fall of Frank Lucas, the most ruthless of Harlem's drug dealers. It's on the long side (the unrated version is 3 hours long), but despite a weak ending it features a great cast, some terrific acting, and some classic scenes.
Best Scene: Denzel Washington gunning down Idris Elba in front of dozens of bystanders.
Six Degrees of Gangster: Denzel also appeared in Training Day, which is #10 below.
Fun Fact: Antoine Fuqua, who would later direct Denzel Washington in Training Day, was signed on to direct this movie before Ridley Scott took over.
5. Casino (1995)
Synopsis: Martin Scorsese directed this operatic take on the less-than-reputable origins of Las Vegas. As much as I like Pesci and De Niro on Goodfellas, I think the interplay between these two aand Sharon Stone makes Casino even better.
Best Scene: Pesci again, telling the banker what he'll do to him if he doesn't get his money back.
Six Degrees of Gangster: Martin Scorsese directed three out of the ten movies listed here.
Fun Fact: Frank "Lefty" Rosenthal, the real-life gambler who served as the basis for Robert DeNiro's character, had the right of approval over Nicholas Pileggi's script.
6. Mystic River (2003)
Synopsis: Clint Eastwood directed this story of three boyhood friends bound together by tragedy. Sean Penn, Kevin Bacon, and Tim Robbins star. It's not as flashy as the other movies here, but it packs a wallop.
Best Scene: The weird, creepy conversation Sean Penn has with his wife at the end of the movie.
Six Degrees of Gangster: Strange as it may seem, I can't think of a single other gangster movie in which Kevin Bacon has appeared. Sean Penn, however, also plays the heavy in Gangster Squad, and Marcia Gay Harden, who plays Tim Robbins' wife, appears in Miller's Crossing. Laurence Fishburne plays another great gangster in Deep Cover.
Fun Fact: Sean Penn won Best Actor, and Tim Robbins won Best Supporting Actor for this movie.
7. Scarface (1983)
Synopsis: Directed by Brian DePalma, with Al Pacino starring as a Cuban refugee who sets himself up as a drug lord in Miami. The 80s syth-heavy soundtrack hasn't aged well, but it's as close as gangster movies come to Greek tragedy. See the extended version if you can. The extra hour adds a lot to the movie.
Best Scene: The chainsaw interrogation. The only scene more over-the-top is the "vice scene" in Casino.
Six Degrees of Gangster: Al Pacino has appeared in A LOT of gangster movies. Robert Loggia (who passed away a couple years ago) also appeared with Jack Nicholson in Prizzi's Honor.
Fun Fact: Many members of Miami's Cuban community were offended by the very idea of this movie, and protested its production in that area. Some even claimed that it was being financed by Fidel Castro.
8. Gangster Squad (2013)
Synopsis: Directed by Ruben Fleischer and starring Josh Brolin and Ryan Gosling, this film centers around a special police unit trying to take down gangster Mickey Cohen in 1940s-era Los Angeles.
Best Scene: The beatdown Mickey Cohen (Sean Penn) receives at the end. Hell yeah.
Six Degrees of Gangster: Josh Brolin also appeared in American Gangster as a corrupt cop. He was also great in both Inherent Vice and Sicario.
Fun Fact: In real life, Mickey Cohen would go to prison for tax evasion. He was charged in 1951 and 1961, without a fistfight ever occurring.
9. Heat (1995)
Synopsis: Michael Mann directed this story of an armored car robbery gone wrong. Al Pacino stars as a detective trying to capture Robert De Niro. It's a very stylized, very austere sort of movie, with a great performance by Val Kilmer.
Best Scene: DeNiro and Pacino talking in the coffee shop. Some of the best acting you'll ever see.
Six Degrees of Gangster: Robert De Niro and Al Pacino's resumes speak for themselves. Tom Sizemore, who plays a member of DeNiro's crew, also appeared in True Romance. Michael Mann also directed Thief, Collateral, and Public Enemies.
Fun Fact: De Niro and Pacino did that coffee shop scene without rehearsing.
10. Training Day (2001)
Synopsis: Directed by Antoine Fuqua, Training Day stars Denzel Washington and Ethan Hawke as a pair of narcotics officers. This movie has to be the worst first day on the job ever.
Best Scene: The part where Washington abandons Hawke in the house full of gangsters.
Six Degrees of Gangster: Real-life former gangsters Snoop Dogg and Doctor Dre appear in this movie.
Fun Fact: Antoine Fuqua would go on to direct Ethan Hawke again in Brooklyn's Finest, a very underrated film.
Honorable Mentions: Road to Perdition, Thief, End of Watch, Miller's Crossing, Day of Atonement, Boyz in the Hood, Deep Cover, American Me, The French Connection, Sicario, Brooklyn's Finest, We Own the Night, The Untouchables, Donnie Brasco, The Dark Knight, The Town, Gangs of New York, Cop Land, Inherent Vice, New Jack City, The King of New York, Bugsy, Colors, Blow, Ghost Dog, and American Hustle.
...and there are probably a hundred other movies that have escaped my mind!
*The book is great, too, and features a whole other character that isn't present in the movies.