Well a clown goby (not a true clown per say) is pretty darn small. I'm not sure of the sizes but the false ocellaris clowns are a more peaceful bunch. I would say any LPS should do fine. I personally love frogspawn, hammer coral, and bubble coral. They all have great movement and are nice to watch, just make sure to give each one room as they can have "sweeper tentacles" and "can" sting each other.