This makes for a nice conversation area that doesn't exclude the rest of the room. Add pillows and throws throughout the room, using an accent color to draw the distinct groupings together with similar tones. You'll want to include some of those same accents in your room's focal point, for continuity. But since you've trained all eyes on that centerpiece, it needs special consideration. As you turn your focus to the room's centerpiece you'll find that treatments for a fireplace mantel will work equally well for an entertainment center.
Books are terrific decorating items.
Books make a statement about you, about your dreams and your life. You may take the paper covers off hardbound books to expose their original colors. Place them on the mantel with candles and plants. This breaks up that straight-plane mantel and creates a more pleasing feel. People are tempted to hang a mirror over a fireplace mantel, but that usually fails to reflect anything of interest.