I know it's barely large enough but I would try a black, jardini, or leichardti arowana with a school of clown loaches.
But since this is in the CA/SA Cichlids section...Geophagus altifrons, Heros sp. rotkeil, Red Spotted Severum, Blue Acara, Aequidens metae, Aequidens patricki, Aequidens sp. aff. tetramerus