How would you feel about gold with tan? It might complement the black couch without making the room too Halloween-ish, and still leave you some options for your artwork. This one is pricey but gives you an idea of what I am suggesting.

Can you move the sofa so it faces the fireplace? It looks a little too close. You could use the rug to frame the living area.

Here are a couple of ideas, not knowing your taste. Moroccan style rugs are a nice trend. There are some inexpensive ones at West Elm. They add some texture and pattern, which I think would look nice with your sofa. Or, go with a warm sisal.

Another option is to go to your local carpet store and have them make a rug for you out of "wall to wall" carpeting. Sometimes it's less expensive. They can bind it for you. Most carpets come in 12' widths. It's a good option if you're renting because you can always have it cut to another size when you move.

Hope this helps a bit.