To truly be earth and human friendly: donate, donate, donate. I can’t stress this enough. If you really want earth friendly favors, donate to your favorite cause and print it up on a small card. I know this doesn’t appeal to a few guests, but your wedding is a fantastic time to do this. I am not, nor are most people I know, someone who expects a gift at your wedding.
If you don’t have a favorite charity, you can find one at Charity Navigator. They rank thousands of charities by financial accountability and such. My personal favorite is World Vision. For E, there is the Hunger Project (they work in Africa). There are also thousands of local options in each city. A soup kitchen would be a great choice. As you and your guests eat and celebrate, you will be providing food for less fortunate people (You can also ask your caterer to donate any leftovers!).
For those of you that really really want to give your guests something small to remember your wedding by, Jennifer at Earth Friendly Weddings has several great ideas. You can find all of them here.
My favorite earth friendly favor are the tree seedlings from Evergreen Memories. There’s something about the seedlings as favors idea that I have always loved. You can see them in action at June Bug Weddings.
Note: WorldVision is a Christian charity. I know this charity will not be for everyone because of spiritual reasons, it just happens to be one of my all time favorites. They have child sponsorship and many other options for sustainable development (you can buy a goat!). They have a high rating and a great reputation. Please feel free to leave your favorite charity in the comments.