Welcome to R2R!!!
Red Pigmy or Yellow Banded Possum Wrasse
McCosker Wrasse
Dart/Firefish
Blue/Green Chromis
Royal Gramma Basslet
Pajama Cardinal Fish
Tailspot Blenny
Flame Hawkfish (my favorite)
Certain Gobies (see below)
In theory, the smaller the fish, the more you can have.
I had a Coral Beauty in a 40 gallon and she did fine. Keep in mind that my tank was 10 gallons larger and I also had TONS of algae for it to eat
Which Gobies depends on the fish/inverts you choose, the amount of sand/live rock you have and how established your tank is.
Make sure you check the compatibility of the fish, temperament and what order they should be added. The more aggressive/territorial should be added last. Here’s a link to a compatibility chart that
@revhtree posted. Definitely check it out!
You may already know this, but don’t forget to QUARANTINE YOUR FISH!! Trust me, I speak from experience. Velvet wiped out my tank last year

Here is a link to some great information on that subject.
Good luck!!
