Pretty much anything except the more aggressive Characins, such as Leporinus (even then, I'm not so sure the Kribs couldn't hold their own). Kribensis are a relatively peaceful species, so they will get along with almost any other fish....
30 gallon, 10 way too small!! They aren't the biggest fish in the world but they need territory if they're to be happy and thrive. This will make them less aggressive toward fellow tankmates.