10 to 55g is a wide range. There are a lot of fish that would do fine in a 55g but go nuts in a 10g due to lack of swimming space.
That said, if you're just looking for some general ideas to help in the decision of choosing a tank size based on fish...
I really enjoy fang blennies. Active throughout the water column and are quite reef safe. Only things that might not be safe with 'em are small ornamental shrimp (such as sexy anemone shrimp), or other fang blennies (unless it's a mated pair). Great for 25g or larger IMHO.
Assessors and possum/pygmy wrasses are also colorful and reef safe. Great for peaceful communities in a 10g or larger.
Currently 5 Chromis, 1 Fire Fish, 2 Skunk Clowns on the way in a 40 gallon. I feel that is maxed out.
Previously in all my nanos and moderately sized tanks (30-45 gallons), always a Clown Fish pair, usually a Royal Gramma, always a Yellow Tail Damsel, Dwarf Angel (usually a Potters or Coral Beauty).
Other fish that have worked a Yellow Watchman Goby, Flame Hawk Fish.
2 black occy clowns
C. lubbocki wrasse
Cf. pylei wrasse
C. brunneus wrasse
Dwarf golden moray
My tank is full. Nutrient wise, I feed several times a day, and I have a problem with low nitrates. My skimmer is rated for a tank twice the size of what I have. Its full from swimming room and territory.