My last set up I had two emerald crabs. They were incredible at ridding the tank of algae, and leaving the corals to be. Until the one just tripled in size and then it liked knocking things over. But it was a character and knew when I came to feed some plant materials.
I am going to look for emerald crabs with my new set up, going for scavengers this week as my new RSM is finishing cycling.
Also very very hardy and colorful purple, orange and white urchin, was a great cleaner. (my avatar is a picture of my newly acquired urchin with my first tank)