Westcott recently released wrinkles-free cloths that are just wonderful, plainly amazing, really. They're expensive but they are much better than muslin because they are really wrinkles-free. They're made of something which looks like polar fleece (is that how it's called in english?) and they can stretch easily. They downside is that they attract dust since they are always prone to static electricity.
That being said, if you prefer to save costs go with muslin. Or drop me a note, I could sell you my black muslin backdrop