Midas gets too big, also Dovii, also probably grammodes?
Then a Texas cichlid ? 
I wouldn't personally...But, that's my 2 cents based on observing other people's fish and doing lots of reading, not keeping them myself. Red texas are unpredictable since they're hybrids...regular texas would need a 75g+, IMO. But they might be OK for a while until they approach their 8-12" max.
Personally, I'd try to put no bigger than an 8" fish in a 55g and that might be pushing it. I've got my CA cichlids in a 75 and they're going to be crowded when they all reach 4+ inches (they'll all max around 5-6) so I will have to pull some out.
Rich, another interesting option if you want unique fish would be a mixed Asian tank with a group of loaches - yoyo loaches, zebra loaches, skunk loaches, kuhli loaches - lots of fascinating patterns to choose from and as long as you don't try clown loaches (too big) or hillstream loaches (unless you want to do a powerhead and high current), they're pretty cheap and fairly unique. I really enjoy watching mine. Add in some other asian fish for the top levels like tiger barbs or denison barbs, and then maybe a centerpiece fish like a gourami (big enough that the barbs won't pick at it, so probably a blue/gold/opaline), and I think it would be a neat tank.
