That question is one the most common we see around here. Most people will say that Head First is enough. Personally, I think it is the only book you need BUT I advise folks to take as many mock exams as they can get their hands on.
You'll find lots of useful information from the links at the topic of our main SCWCD forum page. I recommend reading through our FAQ and then browsing through the Links page for good resources, including the notes of other folks that have already walked this trail.