My Piano Assistant
For Android - The application is a reference of the piano chords and scales. For the requested chord or scale application gives its formula, notes according to a selected root and shows positions of notes on the piano keyboard; it also allows to listen to the selected chord/scale.

GarageBand
Turns your iOS device into a collection of touch Instruments and a full-featured recording studio, a must for all Musicians

Pia Score
Free Music score viewer for iOS - cracking app for reading all your Music - free downloadable classical music from within the app

Smule
Digital Magic Piano

Guitar Tuner
Excellent Guitar Tuner for iOS

MusicNotes
Download sheet Music from musicnotes.com and view all your purchases on this fantastic app for iOS

Songbook
View all your sheet Music in this iOS app

GuitarChords
Learn and look up thousands of guitar chords. Play electric and acoustic guitar on the iPad.

Tab Pro HD
View, hear and play guitar tablatures (more than 200,000 tabs available)

Multi Track Song Recorder
4 track recorder - good for layering up recorded live sounds

Cubasis (£34.99)
Steinberg’s multitouch sequencer for the iPad. Specially designed for quick and easy operation. use for recording, editing and mixing.

Slow Notes
Slow down all your backing tracks without changing the pitch - great for practicing to play along with your accompaniments/backing tracks

Finger Stomp
Great app for playing rhythms games and recording - worth a play!

Orchestra app
Young Person's Guide to the Orchestra

Music Terms
A free dictionary of many foreign musical terms

Name That Note
This app will help you improve your note reading