Recommend an E-Book for the Ipad for PMP exam Prep

 Ok, well I received my eligibily letter, and have about 6 months to left to take the exam.  Changing job locations made studying next to impossible, so now I need to hurry up.  

I'm overseas and don't have an mailing address, I heard the Rita book was good but that's just paperback.  Can someone recommended an ebook from itunes, amazon, barnes and noble, or just send me a .pdf file?

Need something to study other than the PMBOK for two months.  I can get any paperback later when I return.