You mean besides cichlids? A lot of people keep synodontis catfish with mbuna. There's lots to choose from and I suppose they'd be kind of like the kuhlie loaches in your other tank... The only issue with this is that if you are planning on an mbuna set-up (you didn't actualy say what cichlids you're considering), you'll be aware that they don't do well on protein-rich foods. Unfortunately, these protein rich foods are essential for the catfish. Usualy you can get round this by only feeding after the lights go out or by keeping less sensitive cichlids (such as yellow labs which, being insectivores, can handle quite a bit of protein). There's also plenty of pleco species that do fine in african tanks. Things like bristlenoses even tolerate the high pH and hardness. With the more peaceful cichlids, schools of barbs are possible tankmates. Some people have also kept larger loaches with them (such as clown loaches but only in larger tanks) and I've seen an RTBS kept successfuly in a permanent set-up with yellow labs. Of course, you may not even be reffering to rift lake species - pulcher/kribs are also African but live in rivers. You are most probably aware that they can be kept in a semi-aggressive community... That wouldn't be much different compared to the community you described.
BTW, if you want an 'African' tank but don't want to stick to cichlids and want something just as interesting, have you considered ctenopomas? One of the most common, ctenopoma acutirostre, the leopard ctenopoma or leopard bushfish grows to about 6" and is an absolutely beautiful fish filled with character and very rewarding. It can be kept in a community-type set-up with boisterous fish that it cannot fit in its mouth. Larger rainbowfish, loaches or catfish (in tanks where they won't get into each other's way) and larger barbs work fine. There's also a whole host of 'microctenopomas' (don't assume they are smaller though) and smaller ctenopomas and anabas species that you could keep in much smaller tanks and even with small fish like tetras or rasboras.