as well as the dwarf snakeheads as a possible optio, i also mentioned about exodons. they stay pretty small, about 3-4" i think, but im unsure if they would be suitable for your tank. follow the link i gave to the other characins page and search for them. there is lots of pics and info in that section.
tropheus, he decided in the other post that he wanted predatory, aggressive and good looking but nothing he will have to upgrade for in the future.