Most urchins are algae eaters and scavengers, I do not include them in my tanks cause they are also bulldozers. They go all over the rock knocking things over and eating algae.
Some stars will eat inverts, two popular reef safe stars are Linckia sp and Fromia stars. Brittle and serpent stars are also a beneficial addition to reef tanks as part of the clean-up crew.
Sponges are reef safe, but are difficult to care for, you should research then extensively prior to purchasing one.