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: King Robb crawling to the body of his pregnant, dying wife; Catelyn Stark screaming in agony as she watches her son die. Her body hit the floor along with our hopes, and "The Red Wedding" entered the pop-culture lexicon.