the rd should be fine by itself (no other cichlids). plecs are good as darkentity said. you can try giant danios, as long as the red devil is small enough right now so it can grow with the danios. I have danios in with my jd and it seems that the jd just ignores them (don't see any cases of attack on the danios.. ie scars, missing scales/fins) but just makes sure watch it close because your fish may not be as sociable as my jd (he's quite docile as cichlids go)