For me, The Contientious Marine Aquarist takes the cake too.
Clownfishes by Joyce D. Wilkerson is excellent as well and has detailed profiles on the different kinds of clownfish, as well as anemone profiles and care advice. it also contains valuable information about culturing rotifers and other inverts for breeding. Softcover ranges from about $20-25.
For those interested in biotype aquariums, The Natural Reef Aquarium by John Tullock is a good refrence also, and has detailed chapters on each tropical marine ecosystem. Softcover ranges about $25-30.
Marine Fishes by Scott Michael is also a good "atlas" of almost every fish species, containing a page of compact, useful information on each of 500+ species of fish. its great for a quick refrence, especially when out shopping the LFS
and you come across a fish you dont know much about. Soft cover its about $20.