I'm sure others will pop on here with personal experience, but I think the general concensus is that there are no definite answers. It all depends on your betta. Some bettas will get along with other fish, and other bettas will persecute those same fish.
Bettas can present some issues in a community aquarium. First of all, you can have a betta that harasses the other fish, and then vice versa, other fish that harass the betta. You'll notice my 10 gallon is divided right now. This is because when I put the betta in with the killifish, the killifish started biting his fins. Others have had similar problems with tetras biting the betta's fins.
Unless others disagree with me, you could try various different fish (swordtails, tetras), and see how they interact, being prepared to take them back if necessary.
Paul