This one is my personal favorite. Lots of good information and reference pictures. The book shows what a lot of CA Cichlids look like in their purest form, coloration, shape, etc.
The book Manu8_too mentions is also on the top of my list, beside the great photos, it has sections on the different feeding strategies, evolutionary theories, and also talks about what cichlids are found together in nature, and their detailed geographical info.
Of course the names of genera are outdated, but to me that is a minor detail.
Yes, seems everyone wants the Eartheater book.
Like most, the names are a bit archaic, but the basic info still holds up in most cases.
Although I've donated most of my library to the Milwaukee Aquarium Society, it is one of the few books moving with me to Panama.