Like Squawkbert said, I'm amazed that your Betta hasn't chowed down on the shrimp yet.
It's really a shot in the dark because almost any fish will be opportunistic and eat shrimp if given the chance.
I would personally add to your school of cardinals and make that the showpiece, but if you want something different, the rainbows are about the only thing I can think of that are pretty colorful and have small mouths that may not be as apt to gulp the shrimp down.
Let us know what you decide.
