In reply to gimmergimmer:
You would need to have a think about which frequencies are most annoying. Lower frequencies are harder to control.
You can get acoustic panels on amazon. Some look very nice, sort of like a felt material. You can build a frame and put these on the wall as a decoration. If you mount them slightly away fro the wall so there's an air gap, they are more effective. Sound goes through once, bounces off the wall and goes through again. In a frame you could even stack them so they are twice as thick. Then cover in a nice material, to make them look less industrial. You could also mix and match different densities or move the frames around to best effect.
I'd look at parallel surfaces, as theses will reflect sound at certain frequencies, as a standing wave. If you can break these up, with curtains, panels, or furniture, that will help. As well as top of cabinets you can mount them under tables. That will stop some of the sound bouncing off the floor.