drumbit - A very easy to use drum machine.
Music For Makers - Licensing good music has never been this easy.
Remixlive - Remixer, beat maker and finger drumming instrument for iOS.
TunePocket - Download 11,000+ royalty free music tracks and sound FX. Buy once, use forever. New music added daily. Save over 50% compared to most popular similar services. Incredible value!
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.
Incompetech - Royalty Free and Creative Commons Music Archive