There's so many things you can do with that empty space:
Make a large-scale statement, with a textured headboard frame and a dark display shelf for artwork. (Bammaw's House)

 
This intricate decor will bring the focus of your room toward the head of your bed. (Under a Texas Sky)
These were made with fan blades, but almost anything works for the petals. (Diva of DIY)
The wooden white empty frames emphasizes the distressed wooden headboard. (Vintage Headboards)

Read More: http://www.hometalk.com/21915543/s-if-the-space-above-your-headboard-is-blank-here-s-what-you-re-missing