need to know more about your tank before we can suggest any corals.
IE
lighting, filtration, fish, depth of tank, and water parameters. corals unlike fish need a cleaner water to thrive.
Mike
Benificial or easy to keep? The only benificail coral that I know of is xenia which helps with either nitrates of phosphate (forgot which one) they need at least PC's and like dirty water better.
Feduke