How often do you sift through your mail and either recycle or throw away unwanted catalogs? (eh hem LL Bean, Crate and Barrel). While it's nice of companies to often send you free magazines, if you're not going to read it, they don't need to print it!
Simply call them to be removed from future mailings. Not a phone person? Then use Catalog Choice, a free service that allows you to opt-out of catalogs via their website.