Excellent vocoder software for Mac and PC (VST and AU formats), and free and more!
Approximates an analog vocoder hardware side of its fat sound and its imperfections. Much more effective than paying for vocoders with native instruments, or sugar bytes VirSyn I think for the others I have not tried.
Only Eiosis ELS vocoder sounds better and is more complete, this is supposed to emulate a ems 2000 it seems to me, anyway, it is worth seeing.
I can only advise you on the other plug-ins and virtual instruments brand Togu Audio Line which are also excellent ... and freeware.