To put convicts in is a waste of a good tank!
It depends on what you want really. The permitations are vast.
There are alot of nice apistogramma cichlids and rams. They would go well into a planted community tank with cardinal and rummy nose tetras, pencil fish, corydoras catfish and other small tetras. I would suggest only one pair of dwarfs so they have sufficient territory. If you want something a little larger why not try laetacara dorsigera (red breasted flag cichlid) as they are nice and colourful and get to about 100mm (4").
You could try a pair of pelvicachromis taeniatus or subocellatus or humillis or the more common pulcher (krib). They could be mixed with a shoal of congo tetras and other small African tetras/characins. Maybe a small synodontis variety aswell.
There are also nanochromis transvestitus, parilus and nudiceps which could work as an alternative to the pelvicachromis species.
If you fancy tanganikan cichlids you could have a colony of shell dwellers with the large barnicle shells. There are the neolamprologus similis, multifasciatus, meeli, brevis, hecqui, Lamprologus ocellatus and the colour forms of it, altolamprologus calvus too if you want something a little bigger with a few colour varieties to choose from. You could also include neolamprologus leleupi or brichardi although they are not really shell dwellers but could add some extra colour.
I personally would not entertain anything too big as you will be limited to the ammount and types of other fish you can keep with them. I think things like the hero's and cichlasoma's would not be a great choice as they would limit you too much. As regards fire mouths I currently have a pair in my 6'x18"x2' height tank. They are terrorising the other fish. They will be removed and homed in another tank. These things are sent to test us.
I hope this info will be of some use to you.