where in world are looking for your cichlids to be from?
below is just a selection i can think of off the top of my head, there are loads more;
central american - convicts/honduran red points
south american - rams, apistos, keyholes
african - small mbuna (single species only), kribs
just search through the dwarf cichlids listed on google and see what takes your fancy. though remember when choosing its easier to match fish to your tap water than it is to match your water to your fish.
breeding cichlids in a 20 is squeezing them a bit, I know people here successfully breed convicts in small tanks but once the fry grow out and they spawn again you must have a place for those fry to be moved to or they will probably get eaten.