"Words of Love," which is actually their cover of a Buddy Holly song. Just a perfect little song (only 2 1/2 min.) and John's vocals are great. (RIP, John, today of all days.)
Yes, there are about 100 other Beatles songs I could rattle off as favorite, but thought I'd name one you might not have heard. Other obscure-ish Beatles tools I dig: "Baby You're A Rich Man," "Hey Bulldog," "I'm Only Sleeping" and of course "You Know My Name (Look Up the Number)."