What about a dwarf gourami? They get to about 3-4". My full grown one is about 3. And dg's are very colorful. But limit one to a tank. OR, what about a couple bolivian rams or german blue rams? BR's get a little bigger than GBR's. BR's about 3" and gbr's at about 2.5 I think. BR's are not quite as colorful but still a good looking fish. Rams have spunk and I would think be able to hold their own with the barbs.
I'm not sure about mixing any of the suggested fish with the barbs though so I'd wait for some more replies.