Are you going for egglayers or livebearers or both?
Livebearers you could get guppies, platies, mollies, or swordtails. the last two get bigger than the others, so that'll lower the max amount of fish you can half. Just make sure you get 2-3 females per male to spread out the male's attention.
For egglayers you have a wide variety of fish. Some examples:
tetras (neons=> lots of fish addable)
danios
dwarf gouramis
corydoras (suggestable for all community tanks to add life to bottom)
one-two otocinclus
rasboras
You have many from each category to choose from and many other "categories" of fish.
