Tonelib JAM - Create, edit, print and listen to tablature and guitar sheet music
Notation Pad - Notation Pad is the Easiest way to write sheet music with notations on iOS/Android.
Aria Maestosa - Aria Maestosa is an open-source (GPL) midi tracker/editor.
Orpheus App - Sheet Music Reader for Android
Chordsheet Maker - Create chord sheets or lead sheets quick and easily from your iPad. Add rhythms, endings, segno, codas and all what's necessary for your musicians to know what's your music about. Transcription made easy!
Symphony Pro - Complete music notation and composition app for iPad.