ASA Prepware is pretty fantastic. The PPL comes with fixed and rotorcraft question banks and you just pick which one you want to use when you start the questioning. When I bought it, it was 10 bucks.
For the oral, I got the PPLH version of RideReady. It was a great help. It comes with A TON of questions and they are divided into subjects for when you want to study. When you are ready to quiz, it pulls from random subjects. It takes the work out of making flash cards. It was either 30 or 40 bucks.
Both apps are worth it and they work on both the iPhone and iPad.
EB