If you just have one cat, look at getting a litter box that has a cover with a door in the front. We have one right in our living room, literally behind the couch, and as long as its cleaned weekly, I've never noticed the smell.
That said, the best way to keep the litterbox clean is to teach the cat to go outside.
Oh, and if you have any large potted plants in the house, watch out. My wife's cat ruined a very nice 6' tall tree we had in our living room.