Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
OpenMPT - OpenMPT is a popular tracker software for Windows.
MuseScore.org - Create, play back and print beautiful sheet music with free and easy to use music notation software MuseScore. For Windows, Mac and Linux.
Band-in-a-Box - Band-in-a-Box is so easy to use!
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
LilyPond - GNU LilyPond is a computer program for music engraving.