Couple come immediately to mind. One is the old Hank Williams song, "Jambalaya". Everybody knows that chorus, and (bonus) it's a 2-chord song.

Other thing that comes to mind is Ian Tyson's "Some Kind of Fool". It's a basic 3-chord thingy and the chorus is just "La-la la-la ..." all the way through. Good tune and dead simple. I'll send you the lyrics if they're not in the database.