Cucumbers, conchs, cerith snails, and various stars all to differing degrees (generally very little). Most animals sold as detritivores in the hobby are really more like poop buriers than poop eaters. If you've got a problem with accumulating detritus, the best way to deal with it is to siphon it out yourself and work on feeding and flow to keep it from piling up again.
No, it's not true that bumblebee snails eat detritus. They feed on small worms, crustaceans, and other small mollusks.