Well in a 20g I want one betta, and a dozen neon tetras, what else would work good?
Bettas don't do well with that many other fish. Male bettas don't do well with ANY other fish, period. If you get a female betta, sometimes they do all right with cories, large shrimp and large snails. Or, you can do an all female betta sorority. They take some work to set up right, but in a 10 or 20 gallon, you could have a really beautiful tank as long as you follow all the necessary precautions to prevent aggression.