"Your Mother Should Know" is a timeless work of art IMHO. When I first heard it - age 8 or so - it sounded like nothing I had heard before, yet the melody (which doesn't even feature a real chorus) immediately stuck. I then didn't hear the song for many years - my elder brother moved out and, of course, took the Magical Mystery EP with him, it's not a song you would hear on the radio -, but the melody never went out of my head.