I came up with a fun little chain a while back.
EHX Iron Lung vocoder
Big Briar Low Pass
Boss Super Shifter
I run the mic into the iron lung, out to low pass, then to the shifter, then back through the Iron Lung as the carrier of itself.
If the low pass filter wasn't in there this would not work. It would feedback like crazy and probably sound pretty neat before your tweeters exploded. But with just the right settings on the filter it is almost intelligible speech.
I sometimes dial back the crazy on the Iron Lung and the Pitch Shifter so that it is more like human speech. Or take the filter and vocoder out entirely but leave the pitch shift on.
I've done similar set ups with the EHX ring modulator (Full size 'Frequency analyzer'), or the Moog one replacing the Iron Lung.
Basically my goal is a squawking midrange which approximates a vocal but conveys no information. Except when I want actual words to be understood, then I fall back on pitch shifty stuff.