This one is fun (and a little math thrown in for good measure):
http://www.amazon.com/More-Less-Hello-Reader-Level/dp/0590602489
But what has worked best for us, is working with the kids on a regular basis, and picking one thing to focus on for a period of time. It might be an area of the room, like the closet, or a particular category like library books. We also have a very specific checklist for them to follow. Most importantly, I think it has REALLY helped to look around when the room is done and make a big deal of noticing how nice it looks, pointing out specific details done well (“look, no LEGOs in the carpet to hurt your feet at night!”), and how much room they have to play! Nothing so motivating as enjoying a job well done!
