IMO, there are few fish more beautiful than the purple firefish, the regular firefish are no quasimotos either. Most people fint the Royal gramma quite attractive as well as clowns.
I have a 20L reef tank and in it I keep a Redlipped blenny and a maroon clown. I had an African Flameback angel in it until this past mondoy, but it developed a taste for coral polyps and it was necessary to remove it to save the reef.