Hydro power in Iceland, taking advantage of so much falling water. Iceland heats all it's buildings with geothermal and hydropower, the only nation in the world to do so.
However, like most every nation, Iceland has a mixed record on environmental issues. Iceland faces "criticism from environmentalists for its resumption of commercial whaling and single-handedly blocking an international ban on deep-sea trawling, a fishing-method that tears up the sea floor, drastically impacting marine life and ecosystems." However, from the same source "Iceland won top place for its work on environmental public health, combating greenhouse gas emissions, and reforestation."