Zipper quilt back by Frances Moore at frantastic-stitchwitchery: "This is one of my favorite ways to piece a back. Vertical or horizontal, it is fun." I usually don't do piece backs but this one is doable.
This is ingenious! John Flynn's Diagonal backing calculator helps to minimize the amount of fabric needed for your quilt backing. (Flynn was a bridge-building engineer before he became a quilter, and you can tell it from his great tricks.