Modulation Pedals
Chorus, Phaser, Flanger, Tremolo and Vibrato are generally considered as modulation pedals. Depending on which one of those effects you use you can create various psychedelic effects to your music. One of the great musicians who used Chorus effect for their guitars are John Frusciante from the Red Hot Chilli Peppers and David Gilmour from Pink Floyd. Phase 90 was the sound of Eddie Van Halen.