Well, you are going to be somewhat limited with Africans in that small of tank. A 55 is generall considered the minimum due to the crazy aggression of these guys. I have seen it done though as long as you are very careful about your male:female ratio. If you put two males of one species in that small of a tank, you are doomed to have one of them die. Also not enough females and the few you have will get chased to death. You are generally going to want a 3:1 female to male ratio if you end up keeping something like mbunas from Lake Malawi. I can't really recommend keeping these though as they may very well result in disaster in that small of a tank. If you really want these then tell us that and we can talk. My sister-in-law actually has a 29 gallon with some mbunas, but you have to do some very specific things.
One possible alternative is to go with the more peaceful tanganyikan shell-dwellers. You can google shell-dwelling cichlids and see a whole bunch of cichlids. They need less space and are much less aggressive. They each pick out a shell at the bottom and live in it. Therefore, you will have to provide them with alot of shells. Many people love these as they have tons of personality.
Apistogrammas are used in smaller tanks alot, but they are cichlids from South America. It is an option though. You can google Dwarf cichlids to get an idea of these guys and other dwarf cichlid from Africa and South America.
Also, you could try peacocks. They are less aggressive than say the mbunas. Google peacock cichlids and look at all of the different species. There are a billion of them and most of them have really, really bright colors. Peacock tanks can look very cool. You need to research which ones you like first from pictures and then ask back here. We can tell you if they will get to big or are too territorial as there is some variance in this group.
Hopefully this helped.