Have you ever heard of The Beatles Christmas Album?
Released in 1970 through the Beatles fan club, it consists of seven recordings the Beatles sent each year to fans at Christmas. The early records were simply the band thanking their fans and clowning around - but the later ones contained original songs and sketches.
It was never made available in stores. It, and the original singles are super-rare collector's items - although the recordings themselves occasionally pop up on the radio, and are all available on the Internet. (You can also get a bootleg CD of the album on Amazon!)
This recording, from 1967, is probably their best. The song, "Christmas Time (Is Here Again)" was even given a proper release in the '90s as part of the Anthology project.