"The Simple Guide to FW
Aquariums" by David Boruchowitz (TFH Publications, 2001, 243pp).
This is my favorite beginner guide to aquariums. It was written in hope of preventing common newbie mistakes that often turn first-time aquariums into disasters. It contains all the basics about equipment selection, tank cycling, decor, and stocking. There are several suggested stocking schemes provided for 29 and 50 gal
tanks designed to get you up and running headache-free. Plenty of color pics and diagrams. This is a general guide for beginners - no in-depth discussions about diseases or planted tanks.
"The A-Z of Tropical Fish Diseases and Health Problems" by Peter Burgess, Mary Bailey, and Adrian Exell (Howell Press, 1998, 392pp).
This book is a bit more advanced. It starts with a discussion of fish anatomy and physiology. It has a few chapters on water quality, tank size, decor, nutrition, and stocking as they pertain to fish health. The chapter on fish diseases is laid out like an encyclopedia with articles in alphabetical order. It's nice because you can look up a symptom and the article will tell you what may be the possible causes. Lots of color photos.
"Aquarium Fish" by Dick Mills (Dorling Kindersley 1993 304pp).
This is a nice concise pictoral guide to most of the common aquarium fish. Each page provides a thorough profile and color photo of one or two species. I find this book very useful when shopping. There are far more inclusive books out there like Dr. Axelrod's Atlas, Dr Burgess's Atlas, and the multi-volume Baensch Aquarium Atlas, but they are not nearly as portable as this book.
I'm looking for a good book on plants myself, so hopefully you'll get alot of suggestions.