There's no one good book right now... if your budget is limited the specs are good. If you can afford a few books, the Muchow book is a great intro / overview book, but it's a little out of date. The Knudsen book is spotty - good in some places, vague in others. Michael Yuan's book is great in general, although it doesn't cover many areas of the exam - its got a different focus - but where it does cover exam topics it does a good job.
Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)