common livebearers (guppy, molly, platy, swordtail) but most ppl find them boring. I on the other hand love rearing fry since they are SO easy to breed.
It all depends on what type of fish you want, in a community it's usually best to avoid bettas because they do best alone. Another option though, is a sorority tank with female bettas. This is when you mix 6 or more females, you could fit about 8 there, but no more or you'll be overstocked.
Once again it all depends on your preferences.