The new Sanus Elements ELM4 series 1.3b HDMI cables has a connector on every cable which swivels a full 180 degrees. This means that you cable not only will make a 90 degree turn without a problem, but can make lesser turns if necessary to allow access for other cables. The end of the connector is only an inch to the swivel hinge so you should have little problem getting that flat panel right up on the wall.
Discuss "Sanus Elements ELM4 Series HDMI 1.3B Pivoting Connector Cables First Look" here.
Read the article.