The Ring of the Nibelung/Shout-Out

Anime and Manga

 * Giant Robo
 * The Legend of Koizumi features a reincarnated cyborg Wagner as one of Those Wacky Nazis whom our heroes battle, complete with attacks based on his operas.
 * The Yu-Gi-Oh! character, Siegfried von Schroider, is derived from the Wagnerian character, and one of his cards is even called "Nibelung's Ring." Moreover, he has a Valkyrie deck, which is a reference to Walküre.
 * The foundation for The World in the .hack series is based off of this and Norse mythology in general. Several characters also are references.

Film - Animated

 * One of the planned sequences for Walt Disney's Fantasia was the "Ride of the Valkyries."

Film - Live-Action

 * Apocalypse Now: In which, of course, the "Walkürenritt" provides Awesome Music. For further uses of that piece in films, please see that page.
 * Valkyrie: Tom Cruise makes the obvious invocation.
 * In a Musical Gag, the cavalry blacksmith in John Ford's She Wore a Yellow Ribbon is named Wagner; when he appears, the soundtrack plays the smithying Leitmotif from the Ring.

Literature

 * In James Herriot's "All Creatures Great and Small" books, Siegfried Farnon got that name because his father was a fan of Wagner.
 * In George C. Chesbro's The Beasts of Valhalla, Evilutionary Biologist Siegmund Loge (ha ha) is a fanatical Wagner fan.
 * The main character of Robert A. Heinlein's The Cat Who Walks Through Walls also admits to cribbing the plot for one of his books from Der Ring des Nibelungen.
 * In John C. Wright's The Chronicles of Chaos, there is banter mangling together The Lord of the Rings and Der Ring des Nibelungen.
 * Stephen R. Donaldson's The Gap series is literally a Space Opera, being an adaptation of the Ring In Space.
 * George Bernard Shaw’s The Perfect Wagnerite is an analysis of the Ring from a Socialist point of view.
 * In Nicholas Meyer's Sherlock Holmes Pastiche The Seven Per Cent Solution, Holmes (who adores Wagner), Dr. Watson, and Sigmund Freud all attend a performance of Siegfried; Watson and Freud fall asleep.
 * In James Joyce's Ulysses, Stephen Dedalus yells "Nothung!" as he destroys a lamp with his staff.
 * In The Sleeping Beauty, the little bird warns Siegfried not to take the ring or mess with Bruunhilde, saying it will be his "DOOM!" After a book's length of other adventures, Bruunhilde is awakened by a completely different prince, tells Wotan exactly what she thinks of him and the entire story, and informs him that she took the Ring back to the river maidens herself and put an end to the whole silly misunderstanding.

Live-Action TV

 * On an episode of Cheers: Rebecca's wealthy boyfriend promises her a wonderful gift and references a "ring." She gets a desk. Convinced that there's an engagement ring hidden inside, she literally tears the desk apart to find it. Then Sam finds the packing slip, explaining that it's the very valuable and historic desk at which Wagner composed Der Ring des Nibelungen.
 * On Kingdom during a Chase Scene involving Peter Kingdom's Cool Car and a guy on a bike. Lyle puts on the "Ride of the Valkyries."

Music

 * Grave Digger's Rheingold is a Concept Album which is based on The Ring of the Nibelung.

Radio

 * In the aftermath of the Enron disaster, the Firesign Theater compared the Enron story to "The Ring cycle," with hilarious results. A video of that show can be found on the DVD of Enron: The Smartest Guys in the Room.

Theater

 * The great Anna Russell hilariously parodied the Ring in routines like "The Ring of the Nibelungs: An Analysis" [sic] and the Poirot Speak-based "Schreechenrauf."

Video Games

 * In the Sam and Max Freelance Police episode The Tomb of Sammun-Mak, we know that little Amelia Earhart listens to "The Ride of the Valkyries" as a lullaby.
 * The Action RPG Odin Sphere is riddled through with Wagnerian references.

Western Animation

 * In Adventure Time With Finn And Jake, Billy's sword is called Nothung.
 * In Bionicle, the music played when the Le-Matoran are preparing to attack the Nui-Rama Hive is the "Ride of the Valkyries".
 * In an episode of The Simpsons, Mr. Burns gets to fight in a tank ("I've been waiting 25 years for this"), and he plays "The Ride of the Valkyries" as the Awesome Music. He gets Rickrolled.
 * The Looney Tunes short, "What's Opera, Doc?" (and its 1945 precursor, Herr Meets Hare), although most of the music in them is not from the Ring.
 * The Real Ghostbusters had the episode "A Fright at the Opera," in which a performance of Wagner's work gets interrupted by a horde of real (if ghostly) Valkyries.