Waves OVox Vocal ReSynthesis

Very extensive

The menu itself is pretty straightforward but you can really do a lot with this plugin. Would reccomend

Swiss Army Vocoder

Lots of different sound possibilities available and responsive to vocal.

Waves OVox Vocal ReSynthesis

Loads of creative possibilities with OVox, from subtle harmonies to being completely synthetic and robotic sounding. Very intuitive and quick but also very deep to keep on exploring and tweaking.