I assume you are wanting to set up a tank dedicated to fish from Lake Tanganyica? An excellent choice!
A few links to help you out......
http://www.ohiexchange.com/armke/
http://thecichlidtank.cjb.net/
http://www.fishlinkcentral.com/photos/index.htm (I can't help much with the common names but this site gives both the common and scientific names as well as pics of the fish)
First, I have to recommend you get 2-3 Altolamprologus compressiceps or calvus. These are my most favorite of the Tanganyicans. The dwarf A. compressiceps can be kept in a tank as small as 10 gallons. The larger, A. calvus or A. compressiceps are in the 20+ tank range. In all types, the females are about 1/2 to 1/3 the size of the males. Shells are an essential decoration in tanks housing these fish, as the females often take refuge deep inside them where the males are too large to reach. They usually form pairs and spawn in the shells.
Another fish that is one of my favorites is Chalinochromis Brichardi or Masked Brichardi. When mature they are white with a black mask. Very pretty fish. They are a relatively peaceful substrate spawner.
The true shell dwellers are the smaller species of Neolamprologus, i.e. N. brevis, N. caudopunctatus, N. occelatus, N. multifaciatus, N specious. These can kept in tanks as small as 10 gallons. The larger shell dwellers (N. callipterus, N. kungweensis) can be kept in smaller tanks although they will show their natural behavior more readily in tanks over 55 g. There should be at least 2 shells per fish to allow adequate territories for all shell dwelling residents. The shells of the edible snail which can be purchased at delicatessens, are the ideal size and shape for most shell-dwellers.
There is also the Brichardi type Neolamprologus (fairy cichlids), i.e. N. brichardi, N. pulcher "Daffodil"(in my opinion the best looking of the Fairy cichlids), N. falcicula, N. crystiyi, N. gracilis, N. maraguensis. They all have a similar body shape, with extensions off the top and bottom of the caudal fin . All these species are relatively peaceful. They are all substrate spawners.
All other Neolamprologus sp. tend to be more aggressive, and also may attain larger sizes, i.e. N. tretocephalus, N. sexfaciatus, N. faciatus. Most of these Cichlids do best in tanks with a minimum size of 55 gallons.
Julidochromis are the "Slender" Cichlids, from Lake Tanganyika. The dwarf species (J. ornatus, J. transcriptus, J. dickfeldi) can be kept in tanks as small as 10 gallons. The only times one may experience any aggressiveness with the dwarfs is during pair formation. The larger species (J. regani, J. marlieri ) should not be kept in tanks less than a 30 gallon, because of their size and increased aggression. Overall, they are very peaceful with tankmates.
Another group of Tanganyicans that stay relatively small and peaceful are the Xenotilapia (goby cichlids), i.e. X. spiloptera and X. flavipinnis. They should be happy in aquariums as small as 30 gallons. The males can be very aggressive towards each other when courting.
One genus of Tanganyican that you might be tempted to get is the Tropheus. Stay away!! They are very aggressive and unless you plan on getting something larger than a 55 g buying these fish will lead to disaster and despair. This genus contains well over fifty species and variants and are very colorful. There are very few fish that are compatible with the Tropheus, most of them the shell dwelling Neolamprologus or smaller Julidichromis.
For a 55 g any of these will do well with each other with the exception of the Tropheus. You should be able able to house up to twenty fish in a 55 g. Just give plenty of space for the setting up of territories as most of these fish are substrate spawners and can be very aggressive when spawning. Sorry for the length of this post, but I hope some of the info helps.
