Mbuna, any species. My favorites right now are Pseudotropheus demasoni, Labeotropheus fuelleborni (OB), & Pseudotropheus crabro. Now that would be a heck of a setup.
I like them because they are bright and colorful, and interesting in groups. When I had my tank set up I could watch their social interactions for hours, they also recognize when their feeder is in the room and will hide from strangers. I say feeder and not owner, they couldn't care less who owns them but their food provider is their god.