Another plug for Bethesda Systems - they're great. It won't be cheap, but it will be amazing quality.

I cringe everytime I see a TV over the fireplace. Some houses built before the flat screen era even had a space built above the fireplace for larger CRT TVs. So high up that unless you are watching in a recliner facing directly at the TV, very uncomfortable to watch for any extended period of time. It's nice to be able to switch from laying on the couch, sitting on the couch with feet up on the coffee table, etc. With the TV mounted above most fireplaces, it limits your comfortable sitting positions.