If you're going to upgrade the tank size a group of silver dollars would be good. Otherwise, larger tetras like Colombians would work in the 90. Ram's are more bottom-oriented fish, same with most other cichlids. Sailfin mollies would provide some live food if the ire eel would eat the fry, but if not they'll overcrowd the tank eventually. Just about any suitable size species of catfish or pleco would probably work too.