What strikes your fancy? Most cichlids live in large groups in the wild, especially Rift Lake cichlids, and prefer the company of their own kind, so to begin with, I would add a couple more L. caeruleus and a couple more A. sp. (I'm assuming that by Strawberry peacock, you are referring to Dragon's Blood peacock). I would probably rehome the Frontosa also. The 55g will be far too small, as Frontosa get fairly large, prefer to be in groups, and are also from a different lake with different requirements than your Malawi cichlids. THen, with a 55g, you could choose 1 more Malawi species. You could go with an all male tank for color, or a 1m/3f ratio if you want to breed them. You could also add a couple small Synodontus catfish to the tank if you wanted. There are more species than I can mention, but 2 popular species are S. multipunctatus (Cuckoo catfish) and S. cf_polli. Both are active, interesting fish.