A♦ Ace of Diamonds in The Rock Songwriter’s Deck: 52 Ways to Write a Song
The Ace of Diamonds invites you to write new words to the melody of an old folk song.
To avoid copyright troubles, make sure it's really old! Anything created before the year 1899 is sure to be in the public domain. (A few decades later, the era of perpetual copyright began — but don't get me started on the evils of modern copyright law! That's a subject for another day.)
While you're at it, feel free to spruce up the music and make it sound more modern. Sing it syncopated! Add a chorus! Change the chords around! That's the beauty of old folk songs: no one owns them, so you can pretty much do whatever you want with them.