One of my favorite looks is with the use of an area rug. It adds just the touch you're looking for and is an inexpensive option. Here are a few of my favorites.
The easiest way to change the look of any room is to use throw pillows. I constantly change mine. And if you can make them yourself, you can cover ones you already have by just purchasing some fabric!
Now, if you're looking for a more permanent option you can go with something like this wallpaper from Ballard Designs. I think it would be most appropriately used as an accent rather than a whole room.