One ... admittedly very controversial ... thing I would recommend you to consider are amphipods, a.k.a. Scuds.
Snails may be helpful too, but Scuds will do an unbelievable amount of processing and cleaning that neither snails nor corys will do.
Where Scuds are controversial is twofold: 1. they compete aggressively with shrimp often killing many of them, and 2. their addition to a system is basically final -- once they are in there then they are there forever unless you take down the tank and thoroughly sterilize all of it especially the substrate. In nature as well as tanks, what keeps scuds in check are things that eat them ... like cichlids (unless the cichlids are so large they can't care about the comparatively little scuds.) In tanks and other systems where scuds have predators that will happily feast upon them, scuds tend to be an extremely useful addition to the system: reprocessing all sorts of nutrients otherwise left to algae, fungus, and bacteria; stirring up the substrate with deep burrowing; and entertaining and engaging otherwise board fish by giving them something to chase/hunt.
The scud horror-stories pretty much all come from tanks with insufficient scud-predators. Without things to eat them scuds reproduce like a Biblical plague of locust and eventually try to convert all the nutrients in a system into more scuds until their is some sort of Malthusian population limit reached and a spectacular crash of the entire tank/system. As long as there are sufficient critters to hunt and eat them though, the Biblical scud-plague doesn't occur and instead they can do wonders for balancing out a tanks ecosystem.
Isopods are a similar story to amphipods/scuds. If your cichlids are too large to take interest in scuds, then isopods might be a better fit for your tank as they get much larger and thus would interest larger things in eating them. ... Isopods are pretty gross though, but if you have enough hungry and aggressive fish of sufficient size, you shouldn't see them much.
If you want to also add snails I would recommend Malaysian Trumpet snails (go get some of the fancy ones, not the boring/ugly brown ones) and maybe a few Nerites. Depending on the type and size your cichlids though they might make short work of any snails you might add, but at least the Malaysian Trumpet snails can hide under the substrate to at least try and keep their population going in the presence of vicious fish.