The first real book, on Internet Poker, was "Killer Poker Online," by John Vorhaus. It wasn't a strategy book but addressed the environmental differences between online poker and live poker. For example: Before playing live you do many things to prepare; Get dressed, eat, and probably think about the game before you have a seat. Before playing online, many players simply, get up, stop by the toilet, and have a seat in their pajamas. There is a difference. You should prepare to play online just like you might for a live game. Well okay, I guess you don't have to get dressed, but you should probably eat and spend the meal thinking about poker. Vorhaus also addresses some of the situations when you can use the computer as a tool to improve your play. Live you can't very well pull out your calculator or even your notebook, but while playing online you have ready access to both and with some of the helper applications today, even the most mathematically challenged can have access to odds and pot odds, right on their desktop. For many players the ideas discussed by Vorhaus will improve their online game simply by improving the environment.
The best strategy book is probably "Internet Texas Hold'em, Secrets of an Online Pro," by Mathew Hilger. Most recent books include a chapter on Internet poker, but usually the strategies and tactics discussed are simply an adaptation of live play, and few do a good job of addressing some of the situations that often occur online. Hilger's book was written, from start to finish, with Internet Poker as the subject and does a very good job of addressing Internet Poker, instead of simply addressing the differences. If you are an online player this book should definitely be on your bookshelf.
Surprisingly the third book is also by Vorhaus, "Killer Poker Online 2, Advanced Strategies for Crushing the Internet Game." After the original book and the lack of good Internet strategy books I guess it was only natural that Vorhaus write book 2. Although Hilger's book might be a bit better, this one is a very good read and provides some very good insights into the online game. It will improve your Internet Poker.
One final book that was recently published, "Online Ace," by Scott Fischman is also a pretty good book, In fact, it looks like he had access to my notes for about half of it. For the other half, I have no idea where he got those ideas, but it is very hard to argue with success. Many, "old school" players will consider some of the book pipe dreams, but many new young players will embrace it as proven concepts. It looks at poker from a different view. Everyone should read it for insight into how these young guns think.
So the next time you cash out from Full Tilt or Poker Stars , take a little time to surf over to Amazon and pick up a good book. Any of these will give you something to read while finishing breakfast, and before logging on to your favorite site. They will help your game too.