With the most recent update to the iWork suite, users can easily create Arabic electronic books in ePub format and view them on the iPhone and iPad using the iBooks app.
I have tested that and created an Arabic ebook sample, here is a screenshot on iPhone 4:
Another screenshot on the iPad:
Make sure to follow the instructions detailed in this post to generate an ePub file.
Arabic version of this post on SaudiMac Arabic Edition.