Smaller clown species like A. percula, A. ocellaris, or A. perideraion (pink Skunk). Other fishes like Orchid Dottyback (small bright and docile) Fire fish, lots of shrimp gobies (I love Randal shrimp gobies) and their Pistol shrimp partner, Coral Gobies, Jaw fishes, Small angels like Cherub angel, or Flameback angel. There are lots of others fishes that just escape me at the moment.
All of the fish named above are docil and should do well in a 24 g reef aquarium.