Have just got back from Tanzania. By total fluke we found a beach (8km long) with only one small (nine-room) lodge - although they don't trade on their 'eco' side it's the most eco place we've found at a mid range price. Their electric is run on biomass, water is solar heated and the place is built from coco-wood (actually a grass apparently) - totally amazing. They have a website at www.mafiaislandtz.com, get there quick before everyone else discovers it.
Is this your business?