Sunlight streaming through windows can be an annoying distraction. Not to mention the neighbors who have more evening hours to look into your brightly lit living room. You could install shades to foil prying eyes, but swinging wood shutters would definitely be more beautiful.
Interior shutters were the original "window treatments," commonly used in Southern and urban houses, and they're still a great way to add architectural and historical detail. They also help keep out winter's chilly winds or summer's oppressive heat. And they're easy to install on any window because they attach to a thin frame that either sits inside the window opening or around the outside of the casing.
Cost: About $150 to $400.