OG offers ethical volunteering abroad. I highly recommend this organization because of their commitment to ethics, sustainability and the safety of their partners.
I have a friend who did two trips with them and had a really good experience - particularly in regards to ethics."They made sure that we knew our place. Of course, we were helping a little bit, but we received much more than we gave - and it's important to know that".
Okay, I will admit it - this is an expensive organization, which may cause many of you to immediately dismiss it (and that's fine).
They have, however, a range of recommendations on how you can fund your experience and even offer to cover 25% of your fee, if you have the need.