This DIY was on design*sponge not too long ago - maybe you've seen it?
Also, this was on a fashion blog recently, Bobbin Talk
"That's the back of one of my business cards. I recycle cartons from cereal, beer, tea... whatever cardboard I can find to print my cards on! Save the planet one tree at a time!" Aneta Genova
Carrying the recycled concept through all of your packaging and marketing helps to reinforce the green in your work. How do you make your business cards?