Blood red fire shrimp would be my choice. I have skunk cleaners and while cool they love to reach into corals and pull food out of them. Coral banded are interesting and I have kept them also but the blood red fire is much prettier IMO and mine has never bothered corals. Snapping shrimp are cool too but not so much if they aren't paired with a goby which would not be an option in a 5g tank already housing a pair of clowns. They are the ones I have kept, there may be other options I'm not familiar with. All mentioned do need a place in or around the rocks to hide and feel safe so your tank layout would need to allow for that.