Here's another traditional living room with the TV directly over the fireplace. Again, a bit of black around the firebox helps to balance the floating black rectangle. The dark trim around the windows gives balance to the lights and darks in this room as well. Giving the eye something to latch on to and go from object to object really helps. Color is often a unifying element, but in this case, it's the dark tones.
Tip: Be careful not to hang your TV too high or you'll feel like you're in the front row of a movie theater. Lower mantles are better when installing a TV over a fireplace.