i would NOT recommend any haps in a 55 gallon tank. if you are meaning you want mbuna, i like yellow labs, demasonis, johannis, rusties, most of the labidochromis species would work ( i love the color of the perlmutts).
or you could put shellies from lake tanganyika in there (mike would be the guy to ask about those).
i would put about 10 yellow labs and 10 rusties.. just because they are my preferred favorites. and lots of rockwork and hiding spots.
if you want west african/SA fish apistogrammas are quite beautiful and i love rams.
if i were you, id stay clear of kenyis (too aggressive!) and some of the larger mbuna like bumblebees (crabros) empresses and venustus. i had a venustus (a hap) that outgrew a 90 gallon tank by himself.
a group of peacocks would also work (no haps though!)..
best of luck and maybe try narrowing down your list and come back and ask us what would work-there are alot of mbuna to choose from!