5 gallon tank: good betta tank. live plants. Your betta will display beautiful swimming, flaring and exploring behavior in these larger tanks that you may not see when they are kept in smaller habitats.
This is a really hlepful article about setting up a small fish tank. The person actually knows both about caring for fish, and setting up an attractive looking aquarium. Spent 20 minutes looking through my internet history to find again. Pinning, so I don't lose it!