I have noticed clowns mentioned in several of the previous posts, but I am not sure they would fit the bill of the centerpiece fish. I have a pair of Oscellaris that have decided to host in a large patch of Xenia. However, once they chose a host they rarely venture far from it. They are fun to watch if you are looking for them, but they do not come out looking for attention.
I would follow the advice of several above who recommend the Flame Angel. Also a Purple Tang might be a good option.