I like yellow labs but I'm not sure of the other fish that can be housed together.
yellow labs are one of the mellowest of mbunas. they can be housed with either mbunas or haps/peacocks (because they are omnivores, more on this later)
I like Pseudotropheus saulosi
saulosi females have a coloration almost similar to labs (more orange though). only the dominant male will take on the beautiful blue-barred color.
haplochrome Sciaenochromis fryeri, but it doesn't go with mbunas, I think
you are right.
Can you mix haps with mbunas? If not, then why?
the main problem is related to diet. mbunas have to be fed a veggie-based diet because of their long and convoluted intestines. if they are fed mainly protein-based diet, they get the deadly malawi-bloat. the haps/peacocks on the other hand thrive on a protein-based diet.
also, peacocks are much less aggressive than mbunas. some haps are mild, but some haps are even more aggressive than mbunas.
over-crowding works very well with mbunas (with good filtration), because that's how they interact in nature. but it doesn't work that well with haps/peacocks.
but in the end, a lot of people keep them successfully in large enough tanks (or even in a 55g). but its not advisable to do so.
I also like the Aulonocara baenschi or benga peacock
another popular tank is an all-male peacock tank. since the peacock females are all drab and very hard to distinguish, the chances of cross-breeding are very high. and then the fry are not very desirable. so people just have males in a tank. but you can have other haps in there too.
good luck with the tank.