I learned "Black Jack Davy" as a one chord song and still play it that way - words and tune similar to BLCKJCK(2) in DT. I could use more chords than that, mind you, but somehow they never seemed necessary.

Ol' Waylon had a country music hit years ago with "I Don't Think Hank Done It This Way" which always sounded like a one chord song to me.
- Phil