If you want something that will get big and still be happy in a 55 you would probably want something fairly sedentary - Gulper Cat seems like a good suggestion. Polypterus species could also be cool, or maybe a Wolf Fish?
You could get a single Clown Knife? or other solo knife fish. Pretty, entertaining and they eat anything that can fit in their mouth. Alone it should be good. It'll hide at first but should get used to you.
I guess it depends on if you want 1 fish to be awesome.. or a bunch with nice personalities and community activity.
exodons would be cool. looked em up and i like how they swarm around the food.
but either something big and cool, or a bunch of 1 fish thats cool like the exodons. and something active. or atleast kinda active. like my cichlids are out all the time, but they dont swim... they just sit there. theres 2 or 3 that swim every once in a while.
and maybe with the texas cichlid, it was something else, though i thoght thats what it said. looked it up on youtube and it didnt look like that. it kinda looked like a red devil i think. i really dont remember. but these look alot cooler.