Xewton Music Studio for iPod Touch
Xewton Music Studio (XMS) is an amazingly powerful MIDI sequencer with a complete set of instrument samples for the Apple iPod Touch or iPhone. Despite several limitations, this app is quite powerful, very intuitive and loads of fun to use. It is well worth the current $15 list price. I am currently working on my first nOe album using this software almost exclusively for composition. It exports compositions as .wav files and has built in server capabilities which enables you to access the files from you desktop/laptop with a web-browser and download them.