Phaser/Flanger is cool with vocals that aren't scream and/or distorted. Like Haus Arafna,Genocide Organ,Anenzephalia use this effect and it sounds cool.
I don't have a synth but I watched a video of some dude doing vox through a MS-20 and it just sounded like a synth playing to the rhythm of his voice?
i like using panning delay,glitch-stutter delay,lots of the SP-303 effects, and tape manipulations on vocals