Spencer imagines her mysterious life as a black-and-white film noir on Pretty Little Liars.
Cory, Topanga, and the whole gang flashed back to the 1940s on an episode of Boy Meets World that aired during a whole TGIF line-up of retro episodes.
Buffy the Vampire Slayer aired a musical episode, featuring main characters breaking into different style of song. The device was later repeated on other shows...
Among them, Greys Anatomy, which had its characters singing along to songs made famous by being featured previously on the show.
Community is never afraid to experiment, but their stop-motion animation episode was particularly memorable.
Felicity creator J.J. Abrams is such a fan of The Twilight Zone that he themed an episode around the show in 2000.