Keezy Drummer - Make a beat in seconds
Auxy Music Studio - Auxy brings real music creation to iPhone in a simple and inspiring format.
Sampulator - Make (and record) beats on your keyboard
ReSlice - Slice your audio with an advanced, rhythmic arpeggiator and FX.
zMors Modular - Full featured modular synthesizer for iOS
Splice Beat Maker - Make and share beats in your browser