Can be anything from King Arthur, to ancient Egyptian, or some urban legend!
My favorite one is Bloody Mary, and I don't care if it's Halloween or not. You shut the lights out in the room with a mirror, and say Bloody Mary three times. In some versions if you are not afraid she tells you the future, but if you are scared she kills you. In other versions an apparition runs around the room insulting you, and if you last without running away they tell you the future again.
A little bit of dark history the name Bloody Mary is actually based off of Mary Tudor, sister of queen Elizabeth. Mary killed so many people in her reign that the Bloody Mary nickname stuck around until it evolved into it's own myth.
So what is your favorite myth, or legend? Can be from classical literature or it can be a local urban legend.