Buffy the Vampire Slayer - 'Once More, with Feeling' (first aired November 6, 2001)
Joss Whedon's paranormal teen drama / romance / thriller / television phenomenon was well known for playing with convention - season four's almost entirely silent episode 'Hush' won critical acclaim and an Emmy nomination back in 1999. But season six's seventh episode, the awe-inspiring 'Once More, with Feeling', pushed the show into even more exciting territory. Under the influence of demon Sweet (Hinton Battle), the entirety of Sunnydale sporadically breaks out into song and dance, leading to both hilarity and some shocking moments, as long-concealed secrets come spilling out. Musical highlights include the spirited group sing-along 'I've Got a Theory' and Xander and Anya's duet 'I'll Never Tell'.