Medly - Tap & draw to create your song. No musical skills needed.
ReSlice - Slice your audio with an advanced, rhythmic arpeggiator and FX.
Reason Compact - Reason Compact is a smart, creative application that allows users to compose music by inserting great effects or melodies with an easy-to-use command with powerful beating tools.
cassini - Polyphonic Synthesizer for iPhone/iPod touch
AudioKit Synth One - Free & Open-source iPhone/iPad Synth 🎹
nlog Synth - Professional Virtual Analogue Synthesizer ::: check nlogmusic at YouTube :::