I read some common-sense parenting advice in the paper this weekend. Long story short, don't nag. Do.
In other words, if you ask your kids to clean their room, and they don't do it, don't pester them. It is ineffectual and annoys the hell out of you. Instead, clean their room. Thoroughly. Stuff that they think belongs on the floor, but you think belongs in the trash, goes in the trash. You end up with a clean house, without nagging, and they end up (maybe) realizing that if they cleaned their room, you wouldn't steal their stuff.
So today I spent a little time in one of the Sons' bedrooms. The thrift store will be richer today, and quite a lot of scrap paper will be recycled.
I still can't find the source of the stench in there, though. Guess this is a long-term project.