Junk mail (Direct Mailings) are a nuisance. People spend a large amount of time looking through them and disposing them. Massive amount of trees are cut down to make all that junk mail, trees that can be put to better use like providing Oxygen. Many of the trees used in Junk mail are rarer trees that do not recycle well. Another reason to stop junk mail is to make your postal workers job a little easier. I've compiled a list of ways to stop your Junk mail. These are all free. (there are several services that will do this for you for pay but why should you when it can easily be done for free).
There is free do not mail list here: https://www.directmail.com/directory/mail_preference/
To stop Credit Card and Credit Insurance Offers you can call1-888-5OPTOUT (1-888-567-8688) or go to www.optoutprescreen.com required to enter name and address. You do not have to enter your social security number, phone number, and birthday even though they ask for them.
To stop getting Aol discs call 1-800-605-4297.
To stop Publisher's Clearinghouse Sweepstakes call 1-800-645-9242.
To stop American Family Sweepstakes call 1-800-237-2400.
To stop Val-Pak Coupons
To stop sexually explicit mail fill out this form: http://www.usps.gov/websites/depart/inspect/smutmail.htm
To stop catalogs and particular junk mail. Call up the companies customer service center and ask to be removed from their mailing list (have the label handy because they may ask for information from it).
Occasionally first class junk mail can be stopped by crossing out the address and bar code, circle the first class postage and write "refused: return to sender". Then drop it into a mail box.
Another thing you can do to take the prepaid (no postage required) envelopes and stuff them full of paper. Drop in the mailbox. The company will have to pay the postage, this won't stop the junk mail from them but it will cost them some money.
If you fill out a warranty card (mostly a waste of time since they generally aren't required) or give to a charity you should write "do not sell my name or address" or something similiar somewhere on it.
Not everyone lives in the USA but that doesn't mean you can't stop the junk mail.
In the UK go to this site: http://www.mpsonline.org.uk/mpsr/
In Canada, I don't know of a website but you can write to: Do Not Mail Service, c/o Canadian Marketing Association , 1 Concord Gate, Suite 607, North York, ON. M3C 3N6. Tell them you want to be removed from their master mailing list. Include your address, postal code and all the forms of your name that have appeared on your mail.
I don't know about other countries but a web search for stop Junk mail (or Direct Mail) may help you find a way to stop getting so much useless mail.
While you are stopping junk mail you should also consider unsubscribing to any magazines or newspapers that you don't actually read/use. After all they are just taking up room, costing you money, and cutting down perfectly good oxygen producing trees. (If you only occasionally look at a magazine consider looking for the magazine/newspaper online or checking your local library for the magazine/newspaper.)