Earlier this year, Catalog Choice launched MailStop, an iPhone app that lets people take photos of junk mail and send them to Catalog Choice to be put on an opt-out list.

FORBES: Catalog Choice And Its Junk Mail-Zapping App Acquired by TrustedID

The Direct Marketing Association keeps a list of those who sign up at its site to opt-out of direct mail.

FORBES: Yellow Pages: No More Waste on the Stoop