I've seen some really nice decorative boxes that you can put litter boxes in. There is a hole on one side for the cats to go in, but to everyone else, it looks like a piece of furniture. I've seen some homemade ones that were really nice too.

I have one of these and love it (but you can find much nicer ones)
http://www.drsfostersmith.com/produc...&N=2002+113307