I really liked Anthony Calfo's/Bob Fenner's "Reef Invertebrates," and Calfo's "Book of Coral Propagation," 2nd ed. The titles might sound a little misleading, but there was a ton of general aquarium information in both (aside from the title material), that was up-to-date, easy to read/understand, and actually pretty funny in spots (Bob is someone who would be really fun to have a beer or two with). Jay Hemdal's "Advanced Marine Aquarium Techniques" is a little older in context, but Jay is really smart. And of course, Delbeek/Sprung "Reef Aquariums," vol. I (again, or vol. III if you prefer).
Eric Borneman's "Aquarium Corals," and any of Scott Michael's fish stuff for more specific, hobby-related subjects.
Though they are pretty old, any hobbyist could still learn something from Martin Moe's works (plus you can pick them up for next to nothing on ebay and the like).