Even though most junk mail is completely recyclable, it uses a huge amount of time and natural resources to produce. The most environmentally friendly thing to do is to stop it before its produced. This also helps protect your privacy and the sanctity of your home from all those catalogs, coupons you never use, and pre-screened credit card offers. Read more about junk mail from the Federal Trade Commission here.
These web sites can help you get off of mailing lists:
OptOutPrescreen.com (credit card and insurance offers)
dmachoice.org (general direct marketing offers)
directmail.com (national opt-out list)
yellowpagesoptout.com (phone directories)
Catalog Choice (catalogs & direct mail)