Nancy Sinatra, 'You Only Live Twice' (Season 5, Episode 13)
Sure, the James Bond theme about living two lives — now who could that apply to on the show. (If you raised your hand and yelled out "Dick Whitman," congratulations!) The Nancy Sinatra song also adds an air of mystery to this season, which essentially ended on as much of a cliffhanger as Mad Men allows: Don's smoking and drinking at a bar when he's approached by a woman who asks, "Are you alone?" We know he's not; our hero just walked away from helping his wife kick-start her career. But will he stick with that life, or the one of his dreams?