Free app iOS/Android/WP7 app PaperKarma purports to unsubscribe you from junk mail and catalog lists with just a snapshot. You take pictures of your junk mail haul, and PaperKarma identifies the senders and notifies them to leave you the hell alone.
The app says it “can stop most junk mail that is addressed directly to you,” so it’s limited help if you get other people’s crap (I don’t know about you, but most of the junk we get at my house is addressed to former tenants). According to PaperKarma’s Facebook page, though, it will take care of “or current resident” catalogs. And if it works even a percentage of the time, it can reduce the amount of paper going directly from the printing company to your recycling bin, with basically no effort on your part.