I usually make piece backs with some sort of design on the back. I've used stripes of the fabrics from the front, and running brickwork from scraps from the top. Recently, I even used a top that was intended to be the quilt top for the back. I'd purchased a kit of Easy Breezy from a garage sale, and made it up, then felt it was just too plain, so I made a Yellow Brick Road for the front, and used Easy Breezy for the back. They were nearly the perfect sizes, and the fabrics coordinated.
Here is a link to a photo of Easy Breezy. Basically you take a width of fabric, and edge it with piano key strips of coordinating fabrics in various widths. Very fun, and comes together quickly.
http://gobstock.com/easy-breezy-patt...FRFgMgodlxEAcg