The Simple Guide to Freshwater Aquariums - David E. Boruchowitz

Written in a very friendly and simple manner, this book is the perfect starting point for a beginner trying to setup a thriving freshwater aquarium.
Reading this book is a great start for you in this hobby!
Don't be like me. It took me a few years, dozens of tanks and many dead fish until I could finally keep a healthy fish tank for a long period of time. Spare yourself the disappointment of unbalanced aquarium and dead fish, I absolutely recommend reading a good book to get you in the hobby - and I just don't know any book that's better than this one.

Freshwater Aquariums For Dummies

If you don't know where to begin, this book is a very good starting-point.
You will learn the basics of fish-keeping with this fun and easy to read manual.
From the back cover:
"Setting up your first freshwater aquarium can be a daunting task. This friendly guide answers all your questions, from setting up your tank and selecting fish to the water, chemicals, plants, and much more. There's also expanded guidance on combining different species of fish, maintaining a tank, cleaning gravel, and dealing with common problems such as algae."

Encyclopedia of Aquarium & Pond Fish

Over 800 fish are described in this stunning book!
Those beautiful pictures will make you want to investigate and perhaps keep and even breed many fish species you never seen before. This book truly is the perfect gift for someone in the hobby, new or experienced.

Aquarium Plants - Christel Kasselmann

If you just going to buy one book about aquatic plants - make it this one!
With spectacular photos and a very detailed information, this is the best book I have ever owned about aquatic plants.
The book contains valuable information about plants in general - their habitat, morphology, and propagation. Then, a comprehensive encyclopedia of aquatic plant species, each with detailed descriptions and photos.

The 101 Best Aquarium Plants - Mary E. Sweeney

This small book is great to take with you to the aquarium store, so that you can look at it and know which plant to buy.
Basically a beginner reference, it is very good in providing the information you need to pick out the right plants for you.
Good Luck!

Nature Aquarium - Takashi Amano

A real classic! Takashi Amano is a pioneer in the field of planted aquarium, and created a whole type of aquascaping called - Nature Aquarium.
I always enjoy going over this book, every time I start a new project - it's a great inspiration to look at the original work of the master. I recommend looking at many many aquascaping photos when creating a new tank - either in books, or online.
The book contains over 200 vibrant, full-color photos display the captivating beauty of nature aquariums while providing detailed, step-by-step instructions on how to create your own aquatic masterpiece. Along with expert advice on plant and fish selection, water chemistry, and maintenance, the author includes essays outlining aquarium aesthetics and his own personal design philosophies to inspire readers to create their own harmonious and tranquil nature aquarium designs.

You can also try Nature Aquarium World Volume 2 which is also very good (as always with Amano)!

Aquarium Designs Inspired by Nature - Peter Hiscock

You will love this book!
As oppose to Mr. Amano who tries to create a perfect and aesthetic piece of art, Mr.Hiscock focuses on creating a complete natural biotope system. In his designs, the rocks, branches, plants and fish creates a specific biotope found in nature.
Whether it's the Central American stream/rivers, the Amazon acid pools, or the Mangrove swamp, I'm sure you will have a great time creating your own natural biotope.

You can also try Creating a Natural Aquarium (Interpet Handbooks) which is an older and cheaper version of this book.