You should try looking at some of these modern wall planters.

Some wall art ideas.....your dark gray walls provides such a nice backdrop for an art gallery wall....large pieces of artwork or a large grouping of art like these examples below (from West Elm). The last piece shown can (obviously) be hung horizontally or vertically and is also available in a smaller size.

I agree that a media cabinet below your TV would add a nice touch. Also I think a task floor lamp of some sort by the sofa is needed.

Is there enough space to add a buffet cabinet on that wall next to the dining table? These are approx. 17"-18" in depth (from West Elm). This would also be a nice place to add a piece of artwork above.

Instead of a buffet, you could also add a display shelf/bookcase...these are 2 different styles that are not as wide (at 14") as the buffet cabinets posted above and are taller to also help fill in some vertical space.