One fish I really enjoy spotting is the spotted drum. It's not uncommon to find one, but it's infrequently enough where they're not boring.
Spotted drum are about 6-9 inches in length (about 20-something centimeters). If you see one, you will know it. It is an easily recognized fish that is white with broad black stripes in varying directions. The dorsal fin and tail are usually adorned with white spots. If that isn't distinguishable enough, they have a long, white and black "feather" connected on top of their body, between the head and dorsal fin.
Spotted drum are found on coral reefs in the Caribbean, Gulf of Mexico, Florida and the Bahamas. They can be found at all recreational depths. They swim alone, usually under cover of a ledge, coral, or the opening of small caves. For this reason, you will need to get low to find them.
Spotted drum are nocturnal, so it's possible to find them out feeding during a night dive.