Snails, snails and more snails... Nassarius Snails, Margarita Snails, Cerith Snails , maybe some Astraea Snails, and some Nerite Snail. Add a couple of fighting conch too.
Some will tell you add hermit crabs. I don't put things with claws in my tank anymore. The hermits (blue and red legged) always went after the live snails for their shells, even though there were plenty of empty shells around.