Today's movies contain references to films in the past. Not necessarily the best films, but memorable moviemaking that modern filmmakers look to for inspiration.
The art of making movies has been building a cinematic vocabulary for more than a century. Some auteurs revels in the homage; Joss Wheedon, Quentin Tarantino and "The Simpsons", to name but a few. Any film must stand or falls on its own, yet knowing more about the history of cinema helps the film geek appreciate the depth of creation all the more.
Here is my list of films that get referenced a lot. Or maybe other films used the techniques developed for their style. Or maybe a movie inspires another. (No, sequels don't count.) This list is, of necessity. incomplete and subjective.
If you disagree or feel I've left a movie out, you are encouraged to make your own list.