Taken as a whole, the Lord of the Rings trilogy is hard to beat for sheer production. Sure, the storyline of pure fantasy may not appeal to all, but the delivered movies likely has more work put into it than any five other works.
Comedy: The Big Lebowski (and my only one movie to take to a deserted island movie)
Drama: Shawshank
Mafia: Godfather 1 and 2 are tied with an honorable mention to Goodfellas
Action: Also too tough to name one. Hard Boiled, Die Hard 1, Total Recall, Gladiator, Kill Bill Volume 1, Predator, Bourne Identity. Robo Cop, andTerminator 2 all come to mind.
War: Saving Private Ryan and Full Metal Jacket.
Samurai: The Shogun Assassin.
The "don't know how to classify movie: Fight Club.