I read this article a while ago and found it helpful in making a few purchasing decisions recently.
1) I went to Staples to buy some printer paper. There was regular paper, 30% recycled paper, and 100% recycled paper. The more recycled the paper the higher the cost. The 100% recycled paper was $2 more than the regular paper. I voted to purchase the 100% recycled paper because I know that two dollars isn't that much and by supporting the most recycled paper, I'd help create more demand which in turn would reduce the need (however minute) to cut down more trees.
2) We all know Wal-Mart is bad on many levels. In fact, there's a very extensive wiki article on the topic. Down the road was a Target. I voted to support Target.
3) At Target, one of the items on my list was coffee. There were many different types of coffee. At the top was a small section of direct trade coffee. Direct trade in sum allows the most profit for the producer (the coffee farmer in this instance). There are many tragedies coffee farmers face when they decide to sell their product to middle men. Through direct trade, many of these are eliminated while maximizing profit for the farmer. Was the direct trade coffee more expensive? Yes. But that's the cost of justice.