I just stumbled on a guide on How to Stop Receiving Credit Card Offers on Kuro5hin which I definitely need given the aggravating amount of junk mail I get from credit card companies. It begins

Tired of annoying "pre-approved" credit card offers? I sure am. According to the Fair Credit Reporting Act (FCRA) of 1970 as amended in 1996, the four major credit bureaus have the right to sell your information to companies that want to offer you a credit card. Fortunately, the amendment also stipulated that credit bureaus must provide a way for consumers to have their names excluded from pre-approval lists. If you're a United States citizen sick of getting pre-screened credit card offers, this article will show you how to avoid receiving them

Lots of useful information here including a number you can call to opt out of credit card junk mail. According to the article, 1-888-5-OPTOUT is an automated service run jointly by the four main credit bureaus. With one phone call you can opt out of pre-screened mailings from all four bureaus.  Sweet.

A quick Googling confirms the information in the Kuro5hin article which seems to be a summary of the following PDF on the FTC website, Where to Go To "Just Say No"  .