I am a newbie and the first two books I bought were "Aquarium Fish" by Ulrich Schliewen and "Aquarium Plants Manual" by Ines Scheurmann. Both have lots of beautiful photographs of plants and fish and also some good beginner information. The next book I bought was recommended to me by Steve Pituch, "Ecology of The Planted Aquaria" by Dianna Walstad. Its a little more technical but still a wonderful book so far and it came highly recommended.
None. Look at the pretty pictures but ignore the culture sections.
I'm serious, almost everything is either out-of-date/touch or plain wrong (substrate heating is required, nitrate causes algae, etc)... The best all around culture section is in Oriental Aquarium's Handbook, this is available thru the AGA. Walstad's book is a good primer for those interested in soils.
We've come so far in the last 5 years or so in our understanding, most of what we advocate here on the boards isn't in print, all major fish mags with the exception of Aquarium Fish Monthly (Karen Randell writes for this) are hopelessly out of date and written for children - "You want CO2? Good for you! CO2 is a _gas_, which is different from a _liquid_..." *ugh* (FAMA column). Richard Sexton writes for TFH, he advocated a complete breakdown and bleach if hair algae appears!!! Even Kasselmann doesn't mention proper nitrogen levels in water column, macro addition, etc...
I have to agree with Jeff. A lot of the info in the books is woefully inadequate and often misleading.
However, I love books. And for most of us a visual reminder of what a plant looks like can be helpful to incorporate it in a design. My books are within arms reach of the computer so I can check out a plant that I might not be familiar with when someone posts comments about it.
So what books would I recomend? I have two that are seldom listed in recomended book lists. The Baensch Aquarium Atlas (3 volumes) is a great set of books. Good quality photos, most with the subject plant in a aquarium setting. These books seem to list a larger number of overall plants and the photos are good enough to help the average hobbiest to id the plant. How the plants are arranged in the books is sort of strange and I find the culture information to be off base quite frequently. With the large number of plants, relative ease of id, and good quality photos these books, IMO, are a good addition to any beginners library. Oh, they cost about $30 - $35 each so you will have a total investment of about $100. Ouch! However, they have extensive fish listings so you are covered on that base also.
Here is another one - well OK not a book but magazines - Join the Aquatic Gardeners Associtation (AGA). The magazine that comes with membership is pretty good and certainly up to date. While subscribing buy some back issues of Planted Aquarium Magazine (PAM). That mag had some very good info for beginners and experienced aquarists alike.
Another magazine source - this really is my favorite - is to look for copies of the magazine Today's Aquarium. English language verion was available in the mid 80's. I still pick these up every now and then because they are so engaging. I suppose they might seem dated but the pics are great and they travel and show the biotopes. It is a mix of fish and plant articles but it is subtitled "The International Magazine for the Optimum Aquarium" so clearly includes a good amount of plant info. And of course with it's subtitle you can well imagine its bend in thinking. Jim Forshey has many of these mags on his website http://www.seahorses.com/AquariumAndFi****emsForSale/1AQ_MAG.HTM they are $3.50 each.
I include the above recomendations because I think they are overlooked references that can inspire the aquarist even if the information is dated or inaccurate. The downside is that each choice is relatively expensive, or seems that way at the time.
I really enjoyed the books mentioned in the first two replies. For complete newbs to the hobby, they do a decent job of breaking things down so it's understandable. A lot of people out there don't have the slightest clue about plants at all; I work at a pet store where some of the customers can't tell the difference between live and plastic plants. I have to admit that the books mentioned have been almost my only source of info, being somewhat of a newbie myself, and they have really helped me out. I agree that they're pretty low-level and maybe even out of date, but most hobbyists who would find them useful aren't ready for anything too technical... the Walsted book is pretty advanced for people who are still learning about the difference between a rosette and stem plant.
Hopefully, after getting a little experience and learning a bit about the basics of planted tanks, people will look to other places for info, like forums. I'm definitely glad that I happened upon this one the other night...
"Encyclopedia of Aquarium Plants" by Peter Hiscock
I have been into this hobby for about a month, and am now totally hooked (back issues of Planted Aquaria Magazine, The Aquatic Gardner, checking out books on photosynthesis from university library). Sigh.
However, the first book I purchased after first just buying the tank, substrate and filter was the Hiscock book "Encyclopedia of Aquarium Plants." I have rather enjoyed it. I has an easy reading style, very good diagrams, very nice section showing plant profiles with lots of high-quality pictures. I do not think it is a full resource, but excellent for us beginners. I would recommend it.
I second the books already mentioned and also strongly suggest anything by Karen Randall. I wish she had a book. Her writing is clear and fluid and even the topics I think I am not interested in I end up reading because she makes them interesting.
If you scroll down to the bottom of this link you'll find a list of all her articles.