Here is some advice I just gave to another member:
"I have had many tanks over the past few years and you could find a cichlid, or many cichlids in each tank, which ranged from 10 gal to 80 gal. There are some Lake Tanganyikan shell dwellers that max out at 1 1/2 - 2 inches and can be kept in a 10 gal tank. Bigger shell dwells can live in 20 longs or 30 gal tanks provided there is enough shells and cover for them to hide. Just looking at Lake Tanganyikan cichlids, you can find many that will do well in a 50 gal tank. The Malawi cichlids tend to be bigger and have different dominance behaviors which make them unsuitable for 30 gal tanks. Looking at river or New World cichlids, you will find the rams, kribs and apistos, which are all colorful, have varying levels of "meanness" and can live happily in a 30 gal." (*edit--the rams, kribs and apistos should not live together, but multiples of one species can live in a 30 gal).
Bucky Katt, if you want a 30 gallon, look outside Lake Malawi cichlids. You will still find great personalities, wonderful color and interesting behaviors. Although Lake Tanganyikans are harder to find, they are out there and are often over looked. The assortment of body shapes varies more so in the Lake Tanganyikan cichlids than in the Lake Malawi cichlids. If you search this board, you will find the horror stories of keeping Malawi cichlids in a small tank. Here's my story: When I met my husband, he had a 29 gal with cichlids. Then he let me add some. They were all small and cute, which lasted around 6-9 months. Then one hit sexual maturity and suddenly there was our cute tank with dead fish. AA didn't exist back then; we started reading and realized what went wrong. We soon bought an 80 gal tank. That was summer 2003 and I wish we had room for an even larger tank, but we don't.