Super useful electronic chords. The omnichord is a true classic. The only catch is you have to chop them yourself. I just load them into a beat slicer and go to town :). Also sounds amazing with distortion!.
Chord progression (half note open guitar chords) for the widely recorded ragtime influenced song written in 1923 by Jimmy Cox, "Nobody Knows You When You're Down and Out". It features chromaticism through chains of secondary dominants (III = V/V/V/V = V/vi, VI = V/V/V = V/ii, II = V/V, and V) and a secondary diminished seventh chord (viio7/V=♯IVo7).
Example of leading-tone triad (viio) and secondary leading-tone triad in Johann Sebastian Bach's Chorale: Gott der Vater wohn' uns bei (BWV 317). Identified by Forte (1979) ISBN 0-03-020756-8 as BWV 748, which is currently attributed to Johann Gottfried Walther.