North Coast Synthesis Ltd.

Good old vi-IV-I-V

This very popular chord progression is associated with "heroic" moods in classical and film music, but it is also called the "sensitive female" chord progression, and a staple of the Lilith Fair type of singer-songwriter music. The great thing about it for ambient music is that it is endless: it just cycles around and around without ever resolving. It's also easy to voice chords in this progression to move either up or down in pitch according to the mood (demonstrated in my audio clip, and used to good effect in Melissa Etheridge's "Angels Would Fall" where the pitch moves mirror the lyrics). The chords in the clip are Gm-E♭-B♭-F, key of B flat major, but it works in any key. PDF sheet music.