Just a note, Sparkling Gouramis are vastly different from Dwarf Gouramis. There are Dwarf Gouramis (Powder Blues, Flame and Regular) and then there are Honey's which are completely different, smaller and much more passive than Dwarves (Color morphs are Wild type, Golden, Sunset) and then Sparkling and Croaking Gouramis are even small and also very peaceful. More sensitive are the Chocolate Gouramis and the Vaillanti (Samurai) Gourami.
Any of the Apisto's would be great for singles, pairs may be able to fit depending on the type. A single Bolivian Ram may also do.
Gobies would be interesting too.
Most Killifish work great in 10 gallons as well, pretty much any from the Aphyosemion, Epliplaty, or Fundulopanchax would work. Nothobrachius are good too but they are the annual killi's so they only last just about a year but you could get into hatching their eggs, it's pretty simple to do
