Cyphotilapia frontosa is a very large Tanganyikan cichlid, that needs at least a 120g tank for one individual. They reach 15-17" at adulthood, and do well in groups of one male and 3 females. If you like the look of the frontosa,
Neolamprologus sexfaciatus is a similar looking fish that only grows to around 6". Do a search on these fish for more info.
Any of the smaller Tanganyikan cichlids, Malawi mbuna, and some Malawi Haps and Peacocks would be suitable for a 55g. Be sure to research before you buy!
