X-Mas lights (colored or white, but colored is better) look really good. Hang them around the ceiling and you have your "mood" lighting. If you plan on keeping your windows open during the day, then get some plants. A floor rug is a good thing. Get some good looking, comphy chairs. Also, consider getting some of those fold up chairs that go into bags and putting them under the bed. Perfect for large groups.
Get some good looking posters.
Ryan