Snails, fighting conch, some shrimp, serpent star fish, etc. Some would add hermit crabs to this list but they tend to go after the snails and each other for the shells. I'm doing my best not add anything with claws. I still have a bunch a hermits
There are many different species of snails, some will breed in the tank.
Take a look at this package
from JustPhish.com. It's a crabless cleanup crew package.
I've ordered from them last year and was happy with the service. There are many other online retailers with other clean up crew packages.