iGrand is a piano app that has keys as large as the keys on a grand piano (when running on the iPad only). You can change octaves to cover the entire 88 key piano. iGrand can produce seven different waveforms: piano-like, triangle, sine, sawtooth, square wave, cat-derived and horn-derived. You can record and play back up to 7 songs. You can export your songs in the form of MIDI files as email attachments.
Added export to MIDI file, which can be sent as an email attachment.
iPyramid 
iRAW 
iSystem 