SunVox, the cross-platform music creation tracker program that this archive / tutorial site features just got a lot more awesome as its creator, Alexander Zolotov, has ported it to Android.
It can be picked up for just $4.99 - that's a full modular software synthesizer that can export to WAV - available in your pocket. I just now picked up my own copy. Pick it up! Seriously, pick it up.