To me a good area rug brings the space together and acts as art for the floor. It sends a message, "look at me, I'm here and I'm brilliant."
When searching for the perfect area rug you should first determine the size you want, remember it does not have to fit perfectly under all the furniture, but should not be so small that chairs are falling off of it when pulling out from the table. When looking for a rug, don't be afraid to go bold... it's art baby. Let the rug stand on it's own and the furniture be it's compliment. After all a rug is easier to replace than a sofa, two chairs, a coffee table, a few end tables, etc., etc, etc.