We were flipping through Vancouver Magazine and stumbled across the Kattbank bench. This streamlined bench is specifically designed to house a kitty litter box all without your guests seeing, or smelling it.
An opening on the side of the bench allows access to the litter box while a plastic grid removes and catches extra litter from the cat's paws. Finally, holes in the side, not visible from the outside, provide ventilation. Not cheap though, it is available here starting at $1750.