Audulus - A universe of sound at your fingertips - Audulus is a modular music processing app
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Blocs Wave - A free audio app for creating music loops.
cassini - Polyphonic Synthesizer for iPhone/iPod touch
FL Studio Mobile - Create & save multi-track music projects on a smartphone
zMors Modular - Full featured modular synthesizer for iOS