I just tried this one (it lets you preview it, although you must purchase it to be able to save the output).

This sounds much better than vocov213, although it's the opposite extreme in that it gives no flexibility at all.
Unlike almost everything else I looked at, this is a standalone application instead of a plugin, which is okay with me as it's much easier to use.

What I liked is that the words from the modulator signal were very clear and smooth, and the sound was not "all broken up" like what I've experienced with other vocoders. The pitch from the carrier was also very clear, and all pitches in a chord were successfully modulated.

What I did not like is that like most vocoders, it introduces a foreign "robotic" element that's not in the modulator or carrier signal at all. Whereas I have a carrier signal with a very nice tone quality, all that gets scrapped, and instead all one gets is the pitch, and the timbre is replaced with sort of robotic sci-fi sound. One other slight annoyance is that it never remembers where you typically store your files, so each time you have let it to the right directory.

Still, it sounds halfway decent, unlike almost anything else I've come across so far.