If you're in a pinch, on a budget, or just want to have some fun experimenting, you might find that a bed sheet can make an excellent photographic backdrop. Check out this great video that walks you through the process with some examples.
Coming to you from Gavin Hoey of Adorama TV, this video follows him as he experiments with a set of bed sheets as portrait backdrops. As you'll see, weighing down the bottom of the sheet helps to keep it taut and a bit more wrinkle-free; nevertheless, if you intend to use this method seriously, I do recommend buying a simple fabric steamer, which will release the wrinkles fairly quickly and easily. I found it particularly interesting to see how much the aperture changed the rendering of the patterned sheet. At a wider aperture and with a light on it, the effect looks almost like a light with a gobo on it. Of course, though Hoey uses only black, you can use any color you want. A duvet cover might work particularly well: it's thicker, as you don't want light going through the backdrop, and the snaps will make it easier to insert some sort of weight at the bottom. Try it out this weekend!