Sonny and Cher, 'I Got You Babe' (Season 4, Episode 13)
Don's surprise proposal to his secretary Megan at the end of season four comes after a period, following Anna's death, in which he tries to redeem himself. (Poor Dr. Faye, who ends up getting screwed over in the process.) And maybe Don really did think that young, pretty, seemingly carefree Megan would help him, in his words, feel like himself. Of course, we now know that's not true — and the choice of Sonny and Cher's sappy little love tune at the end of the "Tomorrowland" episode seems ironic in retrospect. And lest we forget, Sonny was 11 years older than Cher, and they were collaborators before they were lovers. Coincidence? Doubtful.