The Greatest Filler Episodes Ever
Compiled out of boredom, and in no specific order.
*LOADED WITH SPOILERS, READ AT YOUR OWN RISK!*
"Cosmic Collisions" and "Baseball Blues" (Samurai Champloo)
If anyone knows how to write filler episodes, it's Dai Sato (former writer for Shinichiro Watanabe's previous masterwork, Cowboy Bebop). In these two very different episodes, he lives up to his reputation.
"Cosmic Collisions" allows us to put a face to the voice of the series singing narrator, Heike Shige, and is one part loving tribute to George A. Romero's classic zombie film, two parts fucked-up bullshit. After downing a considerable amount of mushrooms, the gang fall down a massive hole and land in a massive excavation site where Shige digs for the treasure of his ancestors. Desperate for food and money, they decide to assist Shige in his pursuits, but soon realize there is something....odd about him and the many workers. After several mindfucks, two major secrets are revealed, Shige and his men turn out to be long dead and Shige isn't even related to the owner of the treasure they've spent the past 500 years digging for. It all ends with Shige bringing a meteor from the Heavens to kill everyone.
"Baseball Blues" on the other hand is the fucking funniest episode of the whole series. American trade ships come to Japan, and after being turned away, they threaten to attack. After some smooth talk from Kagemaru (a ninja and/or baseball pro), the Americans settle on playing a game of baseball to decide Japan's fate. Inevitably, Mugen ends up getting everyone involved in the chaos and after what may be the bloodiest game of baseball in history, Japan manages to best the Americans.
"Escape From" (Ghost in the Shell: Stand-Alone Complex)
As stated above, Dai Sato is like the Jesus of anime filler. Every series he writes for gets at least one brilliant filler episode. "Escape From" is a real breakaway from the typical GitS formula of "40% cop drama, 50% sci-fi action and 10% genuine wit" for a nice light-hearted day out with a wayward Tachikoma and a little girl looking for her lost dog.
"Heavy Metal Queen" (Cowboy Bebop)
I don't think I need to repeat my thoughts about Dai Sato (who's job in anime was writing for this series). Cowboy Bebop is probably one of the most varied and interesting series ever produced, and this episode never gets the credit it deserves.
With a kickass episode-specific soundtrack, typical 70s kung-fu meets film noir style of series and an episode winning joke involving Faye confusing an ice cream parlor patron for a wanted felon (the scence involves the line "I have a thing for eels."), "Heavy Metal Queen" is one of my personal favorite episodes of any series ever let alone Bebop.
"Kissing Is Such Sweet Sorrow! The Taking of Akane's Lips" (Ranma 1/2)
I never thought it'd be possible to condense the four most epic chapters of the manga into one half-hour episode, but by God, they did it.
This episode is grade-A top quality filler. It adds zero to the plot and is easily ignorable, but still not absolutely insufferable like most modern filler is. It takes a bad sitcom-worthy plot formula (school play gone horribly wrong), adds on some drinking, sword fights and constant changes of pace and cast. The product of this unholy equation? Probably the most entertaining half-hour retelling (read: mangling) of Shakespeare's Romeo and Juliet you'll ever see.
The only things that could have possibly made it better would be the inclusion of a brilliant line from the manga's first chapter (the drama coach refers to Ranma as "The king of crossdressers") and not replacing the slightly lulzy Hikaru Gosunkugi with the horrifically lame Sasuke.
*HOLY SHIT, END SPOILERS!*