Clownfish, gobies, blennies, dotty backs, dwarf puffers or dwarf lions, dwarf angels, cardinalfish, chromis, fairy wrasses, and basslets to name a few.
Just avoid tangs, large angels, triggers, butterflies, eels, large lions, groupers, large puffers, and the like.
It really all comes down to research. Choose your fish selection wisely and know Everything about the animal well before you purchase it - this way, you know that you can meet its size requirements, as well as its dietary needs and water quality requirements.