1. "The Suitcase" (Season 4, Episode 7)
Let's go someplace darker. Don and Peggy pull an all-nighter, from office to diner to bar to office, in a two-person episode that captures all the obsessions of Mad Men: work as drug, work as sex, work as intimacy, work as escape from life, work as refuge from death. Work is for Don what alcohol is for Homer Simpson — the cause of and solution to all life's problems. Peggy finds out she's exactly like Don, like Rosalind Russell bonding with Cary Grant in His Girl Friday. It feels like they're the only two people awake in New York tonight, the only people who'll ever truly understand each other. If I had to watch one hour of TV for the rest of my life, it would be this one. There isn't a single 30-second stretch that isn't perfect. And at the end, Peggy leaves the door open.
Best line: "That's what the money's for."—Don Draper