3. 'The Rains of Castamere' (Season 3, Episode 9)
It's the Red Wedding – 'nuff said. One of the most shocking episode of television ever aired, despite its events being common knowledge to Song of Ice and Fire readers – this could have coasted on the mere horror of losing three main characters in a matter of minutes. Instead, the filmmakers worked to create a sense of mounting dread, ratcheting up the "something's not right" vibe until the knives came out. Then they focused on the grief, starting with King Robb crawling to the body of his pregnant, dying wife and climaxing with Catelyn Stark screaming as she watches her son die. Her body hit the floor along with our hopes, and "The Red Wedding" entered the pop-culture lexicon.