I'm more of a hap guy, so here's mine:
Fossochromis rostratus. The least aggressive of the commonly available 12"+ Malawi cichlids. Males show a blue/purple/black color not found on any other Malawi cichlids. Constantly sifting, moving *LOTS* of sand. Toss in some blue "follower" Placidochromis and watch some really great behavior.
Another gentle giant is the Mara Rocks Protomelas spilonotus. Males get about 10"-12" and by far the least aggressive Protomelas I've kept. They are true open-water haps and will spend a lot of time towards the top of the tank.. I think they're the only Protomelas that is a natural surface feeder.
Arictochromis chrysti is cool in it's shear aggression and destructive capacity as an adult. Their mouth is scaled more like a largemouth bass than a cichlid and that beak is just plain ridiculous.
If you're looking for behavior in haps/peacocks/mbuna, the best way to observe it is to keep species tanks or groups of fish. Otherwise, they're all just pretty single males picking on each other and looking for you to feed them.