A book from Tetra called The Cichlid Aquarium by Paul Loselle is a very good book that gives info on most groups of cichlids you would see in a store or from an ACA auction or something. I think it's around $30. Repair is right that the Aqualogs are good but pricey. The are also geared towards specialists. If you want to look at Central Americans. You have to buy that book. If you want to read about Pike cichlids. That's another book. ect, ect,, ect.......
TFH has some decent books too. Try out the Tetra books that Fieldwalker and I mentioned. You should find all the info you need in them.