Sibelius - Sibelius is a virtual score creation tool which allows composers to easily create new piano scores, developed by Avid.
Chord NOTE - Easily find the right chords to match a melody or musical phrase.
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.
Plugin Boutique - Inspirational MIDI effect that makes finding chords and progressions intuitive and fun
Finale - Finale, the world standard for music notation software, lets you compose, arrange, notate, and print engraver-quality sheet music.
Instachord - MIDI Processing Plugin that helps you play chords and chord progressions faster and easier.