Finatics Aquarium is a good starting point. That store is Cichlid specific as the store is mainly divided between Malawi and Tandanykian Cichlids with a good mix of south American cichlids. My piece of advice is to use caution in selecting your fish. Some cichlids are more aggressive then others. Auratus tend to be nasty to their tank mates. Species 44 are beautifully colored but again they are known to be aggressive to their mates. Also use caution if your breeding. If you get some fish that are aggressive by nature you can bet that they will be extra nasty when they begin spawning as they become territorial. But depending on how many fish you get 500 gallons is plenty of space for the fish to move. My friend unknowingly had a pair of yellow labs (labridichromis) they were calm and peaceful to their tankmates. Yellow Labs by nature are not too aggressive whether they are kept on their own or in groups but once they grew and paired up all the fish were at one end of the tank and would stay there. the pair would not let them cross the center and that's in a 70 gallon tank.
However every tank and fish is different. You wont know for sure if you don't try. Be warned though every failed trail costs money and this can be an expensive hobby :P