free vocoder vst (os x)

i'm wondering if anybody uses a free vocoder vst that they really like. what i'm looking for is a vocoder whose pitch shift value could be midi assigned to a keyboard. it has to be vst because i'm trying to incorporate it into jmelnyk's modded mlr (unless maybe there's an MSP vocoder i could hack it, but i suck at hacking). there are like 10,000 files on the internet that (sort of) fit this description - every one i tried that you don't have to pay for sucks. any advice?