Just released this morning!
Loop based music composition similar to ACID on the PC, but on your phone! You won't find a program like this on iPhone at all.
Preview loops and drag and drop them on the timeline to make tracks
High quality 44Khz Stereo sound engine
Compatible with Android 1.5 and higher
Real time pitch shifting allows you to build melodies
More features to be added soon as well.
Available on the market for $3.99 currently.