Ribbons tied around curtain rings soften the drapery panels. They also help sweeten the room without locking in a specific look. image via here.
A vintage tablecloth with pom-pom fringe becomes a cheerful topper to a kitchen door window treatment. Image via here.
Cut a doorknob set in half, and push each knob into a plastic plug of a curtain rod you've wrapped with ribbon. (You may need to carefully enlarge the plug openings with a drill.
All other images from here.