There are alot of corals you can put in that size tank. Just have to determine your lighting situation, flow, your paramaters, and what you like. If you have good enough lighting for lps and can keep up parameters by either weekly water changes or dosing, hammers, acans, duncans, frogspawn, favia, and candy cane are all good places to start.
If you have a bit dirtier water with nutrients and want a less demanding maintenance with water changes and practically no dosing leathers, zoas, mushrooms, gsp etc would work.