The A.V. Club asked their own staff to name some of their favourite "falling-in-love" movies, and Eternal Sunshine got a mention. If BCK's In box is any indication, it's by far Charlie's most popular film.

Ryan McGee
I'll go for one that is about two people falling back in love at the precise moment that they try and remove any and all feelings for each other. Eternal Sunshine Of The Spotless Mind has a science-fiction conceit atop a living, breathing, beating heart at the center of its near-future tale. It's nominally about a device that purges painful memories from a patient's mind, but seemingly cannot remove them from the patient's heart. It's told in typically loopy, non-linear fashion through Charlie Kaufman's script and Michel Gondry's direction: We see the estranged couple at the end of their relationship, then work backward to rediscover what they once found so appealing in each other. The movie gives the pair an opportunity to start again, but crucially, doesn't guarantee them a happy ending on their second attempt. And yet the couple gladly takes the unknown journey again together, knowing full well how terribly it ended the first time. There's something thrillingly optimistic about that choice, and in the idea that love isn't something you find once, it's something you can potentially rediscover again and again. (Source)

Thanks to Sarah!