For this one I doubled over 2 yards of off-white material and made a balloon valance using 2 strips of black grosgrain ribbon. It actually took me longer to fuss with getting the shape of it right than it did to hang it, and you'd never know that the ribbon has white polka dots on the back of it :)
This was a total "use what you have" mistreatment. The rod was even taken from another window.
It adds a little softness to this corner and the color is similar to the drop cloth drapes in the dining room tying the 2 rooms together. Not bad for $14 and 15 minutes.