Use them to do heavy cleaning with. Use them bunched up to add texture to a painting project, wash them really well and use them to stuff a pillow. Make a quilt out of them, polish metal with them, wrap items up that you are putting in storage for safe keeping. Those are just a few ideas. My suggestion is to be creative and find out how many uses you can find.
Rags are mainly used for cleaning. There are Cotton Rags, Knitted Cotton Rags, Denim Rags, Towel Rags etc. Why not create a range of beautiful rags and offer them for sale on eBay or at a local store in your area.