You can use the MIDI Harmonizer to generate 4-note chords in a seamlessly random manner by playing a single note melody line. Most of the times you would program MH to just hang 3 notes underneath the top note, in many cases the top note being equal to the played (melody) note.
I got a nice example from 'the lensman' that created the following track using the MIDI Harmonizer together with Propellerhead Record/Reason:
Lushly chords are being triggered by playing a slow moving solo line on top of a nice rhythmical cadence. Nice job Mr. Lensman!