I highly, highly recommend Cichlid Room Companion to people.
http://www.cichlidae.com
I realize it's $30 for a yearly subscription, but if nothing else it gives a great photo reference and also has info on where type localities of cichlids occur, etc. They have more info on some species than others, but I still find it's a very valuable resource. I've also heard that Weidner's book is amazing but I cannot bring myself to spend hundreds of dollars on a book (given that you can actually locate a copy).