Depends on the tetras: black skirts, for example, are a menace with long finned fish.
Tetras like neons, cardinals, and glolights are good, loaches are great (kuhlis especially, they are from the similar biotopes), cory catfish, some of the other very peaceful/shy community fish.
Danios, livebearers, gouramis, paradisefish, other bettas, and anything big enough to eat a betta are not good tankmates.