Silkon® Bonded nylon thread works well for crochet. Most beads string well onto this thread, which is a synthetic material that drapes and knots like silk, but resists fraying and has incredible strength. The ends can be seared to prevent unraveling. It comes in light, medium and heavyweight and in a wide variety of colors.
For a heavier look and stiffer drape, waxed cotton cord or twine will give a strong base and is available in various sizes.