Some folks swear by snails, while others swear AT them! Frogs and toads will find your pond in time, as long as it isn't located on a rooftop. Their tadpoles (and toadpoles) eat tiny bits of algae, but probably not enough to make a difference in a really green pond. Dragonflies will lay their eggs on pond plants, as will many other insects. All these creatures contribute to the pond and its surroundings simply by being there. Enjoy them!
John