The Coscinocera hercules or Hercules Moth can reach up to 28 cm wingspan. Which, in my dictionary, means "OMG, that's huge!" This species comes from Papua New Guinea (again, I know. But it's such a unique country!) and North Queensland (Australia), where it inhabits rain forests. They feed on plants, although their larvae consumes most or all of its own discarded skin. The female moths are larger than the males, and live longer than the one or two days the males do - they basically exist only to mate and they're done (poor things!). They are easy prey for many predators, specially the Black Blutcher bird.
By the way, check out their caterpillar! It can reach up to 10 cm, which is quite a considerable size. To see one of them getting out of the cocoon after metamorphosis must be awesome - and a little bit scary if you're afraid of moths.