Ride of the Valkyries (German Walkürenritt) is probably the best known piece by Richard Wagner. It is from Die Walküre (Act III, Scene 1) and has been used to great effect in a wide variety of films, from the helicopter scene in Apocalypse Now to being lampooned in What's Opera, Doc? and The Blues Brothers, to the spa sequence in Fellini's 8½.
Caltech has a tradition of playing Ride of the Valkyries loudly the morning of finals week.