Lapa Rios Ecolodge in the Osa Peninsula is a pioneer in the field of ecotourism and has done some incredible things. Make sure to take the sustainability tour!

Selva Bananito, between Cahuita and Puerto Limon, but inland on the Caribbean side, should also be noted. No electricity, solar panels for warm water for showers, all cabins built from reclaimed lumber, gray wastewater treatment in lily pond. The owner, Jurgen Stern, has a foundation to protect the watershed that supplies drinking water to the city of Limon. He is also active in protecting La Amistad National Park from illegal logging. It's remote, 4 wheel drive is a must and its isolation is a true escape. I was continually amazed at the fantastic food that came from a kitchen w/o power, only cooking via propane.
www.selvabananito.com

Finca Rosa Blanca is an amazing ecolodge! You have to stay there and experience a coffee tour and a bird watching tour. Check this out: www.fincarosablanca.com

We stayed at Lapa Rios for several nights back in 2007 and absolutely loved it. The birding and hiking there made our visit spectacular. You are definitely very far off the beatean path such that you need to order your dinner at breakfast so that they can arrange for it. The food and wine was the best we experienced during our trek to Costa Rica. The only downside was the stifling heat in the rooms at night. Note that it is critical to request one of the low number bungalows because the higher numbered ones provide an exhausting climb to the dining area (hundreds of stairs).