If you want to go a little out on a limb, try rugs (Persian, handwoven, etc.), animal skins, kimonos hung by a dowel through the sleeves, giant platters, big scarves, windows, big plants, other paintings... my attitude is to push for something unusual and have the predictable background as your default setting instead of the other way around.
On the other hand, the two paintings I just started have dull neutral backgrounds, so don't listen to me.
