How long is the tank? If it has the footprint of a 20 long (30 inches), then you may be able to get away with a pair of convicts or firemouths. Keep in mind that convict fry can be hard to unload, due to their very prolific nature. If it has the footprint of a 20 high (24 inches), then you may not. You could keep some African shell dwellers; I've heard that Multies are very interesting to keep, but you would need to make sure to provide the right environment for them with hard, alkaline water and plenty of shells for them.
If you are interested in less aggressive cichlids, you could try a pair of Bolivian rams or blue rams (but not both). They stay small enough so that you could have a small school of tetras for dithers, and some small corys like pygmys or pandas, or some otocinculus for algae control. That would be a cool tank IMO.