None. Fish smaller than a cray WILL become dinner. Fish larger than a cray will eat the cray. There are filter feeding large shrimp that you could keep with docile fish. Atya gabonensis or vampire shrimp and Atya sp or wood shrimp could do well in a peaceful community tank.
Oddball is def right, sometimes even larger fish will get killed and eaten by a sneaky crayfish, Wood shrimp are very cool in a community tank and as little as $4 ea at times. they have very small claws and trippy little mittins they feed with.
Ive been thinking about getting acouple Crays for my 120, but I recently bought a Marble Cat an dont know if he'd try an eat them. Plus I dont know if theyd be mean to my 4-line cats as well as to my marble cat.