Joss Whedon has given Rotten Tomatoes a list of films that echo and mirror his work.
He includes one of my favorites from childhood "The Court Jester" with Danny Kaye, and if you think about Spike and Xander and all the Buffy Puns, not to mention the physical comedy during vampire battles, that makes perfect sense. It's one of those films that stands the test of time as well, because it pokes fun at "serious" films like "Ivanhoe" or any epic about Knights and Ladies and Castles.
Another favorite I share with Whedeon is "Once Upon a Time in the West," a spaghetti western epic starring Henry Fonda as an ultra-evil villain (think Voldemort with a cowboy hat) and Charles Bronson as a cool anti-hero seeking revenge (think Severus Snape). I can see the influence of this movie not only in the western sets of Firefly, but in the sociopathic vampires who barely recall their victims as they destroy one life after another. Chilling!
To me, the thing all these films have in common is that they are character-driven, whether set in the past, present or the future.
You can read his thoughts on each film: Here on Rotten Tomatoes
1. The Matrix
2. Once Upon a Time in the West
3. The Bad and the Beautiful
4. Magnolia
5. The Court Jester
