Since I asked this question on two diffrent forums a few times this week I can tell you the answer. I have a 10, 20 and 30 Gallon, but want to get a 3 Gallon.
1- one male or Female Betta
2- Ghost Shrimp Community
3- 3 Neon Tetra------- Not recomanded since they are schooling fish and are good in a group of 7 or more.
And thats about it.
Also I know the store has it much more stocked and your thinking that looks cute, a few big and small fish in a 3 Gallon, But the store has it WAY OVER STOCKED.
My store has a table with 2.5 3 and 5 gallon tank for sale with fish in them. In the 3 gallon tank the store has a Platy, Barb and 3 Neon Tetras. WAY OVER STOCKED.