Kribensis! Or many of the other non-Rift Lake African cichlids. With cichlids other than rams and some apistos, it is wise to be careful when choosing tankmates. Cichlids are intelligent fishes and their personalities can vary considerably. Some people have good results keeping , say, kribs with standard community species including corydoras catfish. Others (myself included) have found to the extent of lost fish that some kribs are quite aggressive. In a tank the size of a standard 20gal (24" long), DON'T go for any othe lower water dwellers except for upside down catfish or bristlenoses or peckolitas (these are well armoured and nocturnal so won't be bothered by the cichlids). Also be careful with stocking any moderately sized (2.5"+) mid-dwelling fish - I had 2 thicklip gouramis which were killed by the kribs. Small schooling fish like barbs or larger tetras are fine, as are top dwellers including IME and to my suprise guppies.