There have been any number of bluegrass covers of Beatles songs over the years, but the Charles River Valley Boys did it first. The album is called Beatle Country and it was recorded in 1966 and re-released by Rounder Records in 1995.
Beatle Country is just amazing in technical proficiency, wit and beauty. If you love the traditional bluegrass sound (though, technically, this would qualify as newgrass) you owe it to yourself to give this album a listen, even if you're merely indifferent to the Beatles. Conversely, if you're wild about the Beatles but only lukewarm to the bluegrass genre, this album may turn your head around.
Listening to this album, I can't help feeling as if these songs started out as country bluegrass songs; they work so well translated into the genre. I also can't help feeling as if The Charles River Valley Boys are traditional country musicians from Down South, not the Harvard students they actually were.
Especially notable are the toe-tapping rendition of "Paperback Writer" and the comic version of "Yaller Submarine."