Heh, I have a tank with three guppies and a betta and a sword tail. The guppies and betta didn't bother each other, but the betta had to be removed because he was picking on the sword tail who currently has ich. Once his treatment is done, he's going into my other tank and the betta's going back with the guppies.
To be honest with you, bettas vary so much in personality that it depends on the fish. There are some species of fish that are a bad idea to put any betta with. Any tetras that grow over one inch and anthing that is territorial or has the potential to grow big enough to swallow the betta are all bad ideas. Fish that are generally peaceful community fish like small tetras and live bearers are usually okay, even guppies, although the betta may take a disliking to the guppies. What I would recommend is, that if you are intent on having a betta in your community tank, you'd want to remove the tiger barbs first, and try to have a small, back up tank available to put the betta in if there are any squabbles. It can be a simple bowl, just make sure it's at least a gallon. Also be prepared for there to BE squabbles and realize that your betta may not do well in the community tank. They are loners, for the most part, but there are exceptions. I have a betta in a tank with a school of neon tetras and he will actually herd them together. He's rather protective of them and will sometimes flare at something he thinks is threatening them.
Good luck and remember, a little 2.5 gallon tank generally doesn't cost much and is perfect for a betta and an oto or cory, if you really want a betta. They're great fish with lots of personality.
but they will nip his fins like crazy, as will the guppies. Male Bettas can be kept with other fish, I usually have best luck with cory cats and otos and plecos.
