What to do with Junk Snail Mail

What do you do with all those envelopes from credit card companies and magazines?  Do you throw them away without opening them?  That would be better than responding to them for sure.  But that helps fill up landfills in most cases unless you are able to recycle all your paper but that doesn't do anything to discourage the mailings in the first place. 

Of course I wouldn't be writing this if I didn't have a solution.  Take the Business Reply Envelopes and fill them with all the contents of the envelope along with the envelope it came in and mail it back to them.