The Rutles was a 1978 TV movie originally titled "All You Need is Cash." It is a spoof documentary of the Beatles' story. It was made by and stars Eric Idle from Monty Python. He plays the narrator/interviewer of the story, as well as one of the Rutles. Neil Innis also plays a Rutle and I think wrote most of the songs.
Not only is the movie funny as f-k, it is thorough in that it leaves no Beatle legend unspoofed. For instance, the John Lennon character causes a scandal when he declares that the Rutles are "Bigger than God." But it turns out he was misquoted -- he said "bigger than Rod" -- Rod Stewart, who wouldn't be famous for several more years. The songs are parodied perfectly too -- "Get Back" is "Get Up and Go Back Home," etc.
Think Monty Python combined with Saturday Night Live with some Spinal Tap elements. Besides Idle, there are numerous cameos -- Michael Palin, John Belushi, Bill Murray, Gilda Radner, Dan Ackroyd, Mick Jagger plays himself (commenting on the influence of the Rutles), and George Harrison appears in there somewhere as well.
By all means buy/rent/download this movie.