Difficult to say, about the tank mates...especially since most sharks feed on flounder and other small, bottom dwelling fish. I also would not risk a scirmish, between a shark and a ray...they'll compete for food and the sharks will most likely take a swipe at a ray.
Port Jacksons and Horns have already been mentioned. Leopards, to my knowledge, are still illegal (under a certain length) and reach lengths of 6'+.
Other than already mentioned, there aren't really too many (that are available in the hobby) that come to mind.
In a tank, the size you're talking about, I'd get a pair of Ports and a pair of Horns. They'd thrive in the size habitat you're thinking about and both reproduce quite easily, in captivity.