The islands of Raja Ampat are right in the middle of the center of diversity of coral reefs and reef fish in the Indo-Pacific; it is hard to come up with a better reason than that to include anything in the list of World Heritage. I visited on board a ship dedicated to scuba diving, and boy was it ever worth it. The reefs are almost pristine, mostly because there are no large cities nearby and so there isn't much runoff or (many) fishermen. Huge schools of fish, both small and colourful and also very large (snappers the size of Volkswagens!), sea snakes, dugongs, sea turtles. Oh, an on land there are birds of paradise, too. An amazing place.