marbled crays would be great they are very docile. more than likely to breed as they can clone themselves, they will lay tons of eggs over time but that shouldnt be a problem as ur cichlids will gobble them right up. mystery snails, u can remove the eggs they have above water. nerlite snails wont breed at all in freshwater they need brackish. clams, they will rape your tank with babys though, they are really neat though, they will sell pretty good as well. bamboo shrimp are neat to they are filter feeders, they would be too big for ur cichlids to eat (i think) they get about 4" from what ive heard. all depends on what crabs and what cichlids u have and how big they r.