Chord NOTE - Easily find the right chords to match a melody or musical phrase.
Captain Chords - Write chord progressions in your favorite DAW
Plugin Boutique - Inspirational MIDI effect that makes finding chords and progressions intuitive and fun
RapidComposer - MusicDevelopments RapidComposer: Music Prototyping and Automated Composition Software
Instachord - MIDI Processing Plugin that helps you play chords and chord progressions faster and easier.
Cthulhu - VST MIDI-FX plugin for harmonic inspiration