OK, in a 2 foot tank you're looking at a fish that is about 4 inches long. How about a trio of betta imbellis (1M, 2F) or a single giant betta splendens?
Anything larger won't be suitable.
Do you plan to have any other fish in there or just the one?
I would try to keep a rainbow cichlid alone in a tank that size. In such a small tank, I would not try to place anything else with him. They typically grow to 4 or 5 inches long as adults. This is some of mine in a much larger tank. I did keep them all in a 29 gallon tank the first 6 months I had them but now they are the showpiece in my 125 gallon tank.