I currently have 2x angelfish and 4x pearl gouramis as the larger denizens of my 120g. Take a look at some of the larger rainbowfish as well. We had 3x goyder river trifasciatas that I loved but were casualties of a can filter failure. Those are probably a bit large for a 50g. Turquoises and Irian Reds don't tend to get as big so quickly and may work in small number of 4-5. Hope that helps and interested to see what you decide.
Bolivian Rams, Keyholes, Port Acara, Flag Acara - lots of small/med Cichlids to choose from. Or maybe a school of different shaped tetras like Bleeding Hearts. For something more unusual maybe a small group of Spotted Headstanders.