So I know there have been debates on here about donating to charity as a wedding favor, so I thought I'd chime in: I found a website (tisbest.org) where I could buy charity gift cards that allow the recipient to pick the charity (from a list of more than 300). I had charity cards made up with me and my now-husband's photo on them and gave them as favors. I get emails whenever they're redeemed -- the emails tell me which charity they picked. These were really well-received and it's been fun to learn about the charities that the people around me care about. And then they have a little photo of me and my husband if they want to keep it.
Okay, just thought I'd mention this website as it's a good charity option I think. I wanted to do something charitable, but I didn't want to choose the charity FOR someone else (since everyone has different ideas about that). This was a fun alternative I think.