I used the NCEES practice exam, material from a review class I took at a local university and also the PPI reference and practice questions and NEC. I had a few other books but I don't think I used them on the test.
Here was my basic study plan:
Review coarse (it forces you to think about it and spend time working problems), work problems, work more problem,....... Take sample exam (Not all in one sitting, a few questions a day). Check answers. Try to understand what you did wrong on any missed questions (there was a forum I used for some help but I can't remember the name). Move on to the the next wrong questions. Once you understand why you missed the questions. Retake the exam but only work the missed questions. Continue this process until you correctly work all the problems (or most), Take practice exam from another reference using the same procedure. Keep all the correctly worked questions for a reference.