Throughout the movie, many different characters either sing the words to or hum the song "Danke Schoen". Ferris sings the words in the shower, Mr. Rooney hums it while he is waiting in front of the Bueller's house's door, Jeanie sings it while she is running down the stairs after she kisses Charlie Sheen, and Ferris sings it again during the parade.
A punk rock band named Save Ferris got their name from this film. During the film we see several "Save Ferris" references.
A common misconception is Ed Rooney is the Principal. He is actually Dean of Students and not the principal.