I am looking for the one good book to read for Automated Testing in general of a website.
If your definition of Automated Testing includes or is the same as Unit Testing (the terms are sometimes used interchangeably), then I'd recommend Pragmatic Unit Testing. It doesn't go into the depths of test frameworks, but it's more of a study on the whys and wherefores of Unit Testing, and how to make unit testing work for you.
There is a good selection of automated testing books at SQA Forums. One book dedicated to website automation is Automated Web Testing Toolkit. However you will find that most test automation best practices and techniques can be applied to multiple technologies. So I would recommend taking a look at Automated Software Testing by Dustin, Raska and Paul. Also note that Dustin is working on a new book, Implementing Automated Software Testing.
The Art of Unit Testing - "The art of creating Readable, Maintainable and trustworthy tests" by Roy Osherove
"Unlike other books on this topic, this book trades theory for real-world examples. It's designed so that you, a working developer, can start writing better unit tests now."
http://www.artofunittesting.com/
Chapter One, The Basics Of Unit Testing, is available as a free download from the above site if you want to "try before you buy"