ireal book is probably the best app around for me. I'm typing in loads of the tunes I play and it is a great help with practising. I also have iGigbook, pdf sheet music setlist maker and music notes. none of which I have managed either to figure out or find a use for. Nor, in a a continuing flush of enthusiasm with my new iPad have I used the three metronome apps I bought, although Pocket Piano is quite fun and a friend of mine has an Ocarina app that you play by blowing into the mic on you iPhone.