Oh, yeah, porcelain "crabs" are a good alternative. They don't eat algae, but they're neat. Green ones can be kept in small groups, white ones (porcelain anemone crabs) should have an anemone of some form to host, but are very pretty and fun to watch. Their claws are mostly for display, they primarily filter-feed (though you can give them larger chunks of food to keep them healthy), and they lack the ability or the gumption to go after tankmates.
Other animals to avoid are, yes, Sally lightfoots, arrow crabs, and coral banded shrimp. Little ones may work (the smaller species of CBS are generally fine), but once they grow you start to have problems. Things with claws tend to use those claws.
