A male betta should get along well with any fish normally described as "peaceful". Mine has been living quietly with Platys, Neons, Corys and (recently) two Dwarf Gouramis. Everyone pretty much ignores everyone else.
If I were starting a community tank today I would choose Platys, Mollies, Corys and Gouramis. Danios would be on the list if the tank were big enough for these fast graceful swimmers. Neons are pretty but unless you have a dozen or so you have to stand very close to the tank to see them.