I keep coming back to grisaille wallpapers and murals, probably because of their monochromatic grays.
Not sure where this example (above) is from but it's probably pretty old. I am loving the more modern interpretations of grisaille we're seeing lately...
While not exactly grisaille, the drawing Lauren Liess had blown up for her dining room wall gives the same effect.
And this paper panel from Anthropologie is another fresh take on grisaille. I could totally see it in a room with a few modern pieces.