I'd recommend the FAR/AIM 2008 :laff:
Seriously though:
PHAK: Pilots Handbook of Aeronautical Knowledge
AWS: Aviation Weather Services (make sure its the NEW version that came out 2 weeks ago)
AW: Aviation Weather (they sell the AWS and AW book as a set. I'd go for that.
Everything Explained For The Professional Pilot : The 5th Edition
Private Pilot Oral Exam Guide
FAR/AIM 2008
Get all of those, and you'll be quite set for your Private, Commercial, and even your CFI. All of the books I listed MINUS the Everything Explained CAN be used on the CFI Oral part of your checkride once you get there.
For Instrument... check out the Instrument Procedures handbook issed by the FAA.