If you don't have the betta yet, you can pick out a pretty passive one at the store and hold his little cup up to the tanks of fish to make sure he doesn't flare at them. They should do okay with tetras, rasboras, a big school of danios (big enough that they don't pick on the betta), any bottom feeders aside from sharks, probably some other things too. Unless it was a REALLY big tank, you wouldn't want a male with any other bettas, including females.
Female bettas give you a lot more leeway. They can go with pretty much any community fish. You can even have a group of them, just make sure you've got enough plants and decorations and stuff in the tank for them to each make a territory.