I look for flannel sheets to use for backing and if not in great shape color wise..use for batting in small projects.
I also use material that I find that I may not really like...large florals or whatever to use for backing.
My quilting teacher has some of the prettiest backs to her quilt using scrap pieces and odd blocks...like getting two in one. I love that Idea. So I always after my first two try to be creative with my backs.