you could probably do the smaller mbuna.
Examples: cynotilapia afra (all varieties), Psuedotropheous salousi is a good one too.
You could try Pseduotropheus demansi.. but you need a group of around 10 to help keep agression down.
Less aggressive mbuna: yellow labs, acei (keep in mind though, eventually acei get quite large).. Other labidichromis are also mellow in my experience (have not had them all though).
I am sure there are more, that is what I can think of off the top of my head.
You might also want to think about doing some Tangs, especially if you want to trade or sell them to other people.. A little more difficult to spawn, but more in demand, and more choices for smaller ones..