Official Guides of course, are a must. They're the best book out there only because they're the people who make the test, so they know what they're talking about.
I agree that Manhattan Review
books are great. I had them when when I took their course right before my GMATs and they helped a lot. They update these books frequently so that's always a good thing. Make sure you get the newest one.
I did have the PR books. I didn't think they were that great, but they were alright if you need brush up on your basic skills.