drumbit - A very easy to use drum machine.
Sampulator - Make (and record) beats on your keyboard
Remixlive - Remixer, beat maker and finger drumming instrument for iOS.
Tinkersynth - Create and purchase unique generative art
Hip-Hop Producer Pads - Hip-Hop Producer Pads is an elegant mobile app that works as a drum machine and helps you to create beats and rhythm right on your mobile devices.
Splice Beat Maker - Make and share beats in your browser