I have been dreaming of having a decent vocoder for years. And finally here is a good sounding, highly functional answer to that wish! Vokko has a very efficient synthesis engine on it w/ 3 oscelators (1 PWM, 1 rompler style, and 1 noise) which produces a great variety of carrier sounds. It also can do soundfont playback as a carrier as well, but I have not messed with that feature yet, so I can't comment on it. The interface could be a little cleaner, but it is usable. And certainly the most gratifying thing about it is that you get to install it, load it up in your host, and instantly start vocoding. I am running Sonar 4 as my host and I have managed to crash it a few times when using this plugin, so I think it could be more stable, but it is fun enough for me to put up with the crashes. Perhaps other hosts would be more stable.
This thing produces very nice sounding vocoding effects, vocal modulation sources result in highly comprensible results as long as you use the proper carrier synth settings. Other uses other than vocals (drums, random experimentation, etc.) also sounds great. The manual is not too well written and a little jumbled, but the user interface is simple enough that a quick look thru the manual is about all you'll ever need to get it. A lot of the features seem to be overkill to me, apparently it is based on someone else's vocoder effect and then other modules (such as the soundfont player) were added to make this into a new instrument. I haven't really bothered with the filters or envelopes, since I am using this mainly for vocoding vocals at this time. Many of the features seem extraneous to the core purpose of this instrument, but then again maybe I am just not using it the way the designer intended.
One thing to note is that the price for Vokko is $30US, not the $15 indicated above. That was the price I was charged for it as of 04-11-1 at least. But still, $30 is a great price for this handy little tool if you don't have a vocoder feature rolled up into some other plugin that you already have. This is a great sounding piece of dedicated software.