I agree that you don't have to buy a book, but I think its absolutely worth buying at least one book per exam. Most of the people I've seen that fail badly do so because they look at the exam title and prepare based on that, rather than looking at the requirements that MS has assigned to the exam. The book goes one level deeper by trying to teach you only what you need to know to meet those objectives. $40 for a book is not a huge investment, and you can probably make back $10 selling it used. The books usually contain sample questions which while probably not as good as the Transcender ones, arent bad either.