Junkbusters has a free service, Declare, which should help to reduce your junk mail.
Private Citizen has a more extensive paid service. For $20 a year they will list you in a directory that goes to junk mail firms, which allows you to sue them if they call you. More than $2 million has been collected from sued firms and most report a dramatic reduction in junk phone calls.
They also have a similar service for $10 a year for junk mail, which works quite effectively.
Private Citizen July 3, 2003