My favorite Beatles song is "Long Long Long" off the White Album. It was written by George Harrison. John Lennon doesn't even appear on it.
While the mono version is great, I especially love the S P A C E created by the stereo mix. Such great instrument separation and panoramic positioning. I love how the Beatles often used the studio as a songwriting tool; here, the rattling heard at the end of the song is the result of a wine bottle sitting on a Leslie speaker and getting harmonically excited by notes played by McCartney's Hammond organ.
It's perhaps the most underrated Beatles song, and part of the reason I love it so.
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Long Long Long" (Stereo)
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Long Long Long" (Mono)
BONUS: Low also covered this song to great effect.