I have it on good authority that the site optoutprescreen.com is a legitimate and fairly successful way to opt out of all sorts of junk mail.
First, the site is mentioned on the FTC’s site as a way to reduce the amount of unsolicited credit and insurance offers.
Second, Ed Foster researched the site and found that it was legitimate.
Third, I just did the online request which gets me 5 years and I’ll be mailing out the other request to get the permanent opt out. Then I’ll wait and see if the amount of junk mail decreases and let you know.