What curtains to buy?

With beige walls and black sofa you can use the curtains to add an injection of compliemtary colour to your room. I would suggest black curtains with a lime green or hot pink stripe or small patttern, that way you could pick up that colour in new cushions or a rug to add colour to your room. As the curtains are quite long I would suggest a small, rather than large pattern as it could take over the room.