I just thought of a lovely one: "Lavender's Blue." this was first recorded sometime in the 1500's, and we are still singing it today.

William Cole has a collection of Great-British folksongs which is to be found in many libraries. His old "Lavender's Blue" has rather sexy (and touching) words to it.

I've wondered whether the "dilly" of this song is related to the "dil" in dildo, but my unabridged dictionary got all embarrassed and refused further enlightenment when I starting tracking down the word origins.