I used both the Pad Pilot (Slate-Ed Inc.) and the Jeppesen "books" available in the iTunes store. Pad Pilot is fairly basic compared the Jeppesen, but helped clear up some issues I had as well as being alot easier to read (ie. aeronautical weather for dummies, which btw, I am one of...).
I also liked reviewing with the information found here:
www.TheAirlinePilots.com :: Index .