There is no such thing as a good tank mate for Cephalopods they eat everything. And unless your extreamly lucky they will kill any other Cephalopods you add to their tanks.
I wouldn't put anything with a cephalopod. But if you really want to try go to the http://www.tonmo.com/ forum and ask them they would be the ones who could give you the best answer, but again I would be surprized if you can put anything with them.