here I am!
Unfortunately you are very limited. The 20 is a long or a tall? I'm going to assume, until I am corrected, that it is a tall.
As far as New World cichlids go you don't have much choice. Apistogramma and Rams are about it. The benefit of these guys, as mentioned already, is that you have the option of other non cichlid tankmates.
You also have the option of a small Tanganyikan African set up. You can do one pair of shell dwellers along with one pair of small rock dwellers like Dwarf Comprecisseps, Caudopuncatus, or Lepidiolamprologus hecqui. In addition you can likely get away with a few danios and a bristlenose pleco with them. If this interests you then you should definetly start some research on Tanganyikan cichlids, and I can help you in greater detail as well.
The fact is that cichlids require space, and the more space that can be provided, the more rewarding they are to keep.