Here's a clever way to hide those pesky cords and cables from a wall-mounted TV: use wall trim.
The Sawdust Girl blog offers this tutorial. The trim work hides the cable cord, an HDMI cord and the TV's power cord. Although it's not a great idea to mount your television over a fireplace, this project is another way to hide unsightly cables.
How to Hide TV Cords in Trim Work — Guest Post [Sawdust Girl]