Could do a pair of Honduran red points, pair of kribs, a group of shellies, pair of rams and some dithers, single acara maybe, piar of apistogramma, gourami community, giant betta community (single male with tank mates), single angelfish if the tank is tall enough, single male convict, single Roman numeral cichlids (not seen often), single female t-bar.
In no way am i suggesting all of these fish together.
Basically if you want a single fish you want to aim for about the 4 inch range. Smaller if you want other fish with it.