What fish do you currently have ?
My favorite fish was my flame angel. They are excellent looking, free swimmers and get along well with other fish.
They have a 50% chance of nipping corals though.
Other great fish are Clown fish, Firefish, Lawnmower blennies. Maybe a six line wrasse is an option as well.
Damsels are good looking but very aggressive and should be introduced to the tank last.