I personally love flame angels, which also stay small. However, in a tank like that I would get an anemone and put a pair of clowns in. Maybe a cleaner or some other shrimp wo clean, but the two clowns hanging out in the anemone would be ausome.
I have always wanted to do this, but just havn't gotten around to it. Now that I have a decent size lion, my fish need to be bigger.
Good luck with what ever you decide!