Dario darios are a GREAT suggestion! (Scarlet Badis)k
Or, you could have a heavily planted tank with a breeding colony of cherry shrimp. You can have like 150 of them in a ten gallon!
Here's mine. Ignore the breeder box in there, my corycats laid eggs again, and this time I had time to scrape them off before the cories munched them! My regular hatching/rearing tank has some senegal bichir growing out, so the shrimp tank was the best option!