I have a Zebra Moray Eel that has been for the most part a very model citizen in regards to other fish inhabitants. I've only witnessed our eel snatch a hermit crab that was walking by and partially crush it's shell, but with luck it survived the ordeal. Recommended with planning.
Another is our One Spot Foxface. I've only witnessed it mow down a large colony of pulsing xenias, guessing 6+ months ago. Since then, have had no issues. Was worried for a bit as to what the next coral it was looking to snack on, but nothing else has been targeted to date. Not sure I would get another after this one, but really on the fence on it. Maybe later on if upgraded to a larger system, then may lean towards getting another.