Chris is right. The Digitech Talker is amazing. I got one from Ebay for $200; had I been more patient I could have gotten one for $160. The only other vocoder I have is the Boss VF-1. It has a 10-band vocoder that needs a little tweaking but sounds fairly good. The VF-1 is a multi-effects unit that does many many things; vocoder is one of them, so it's not the best, but it is really quite good and intelligible. The digitech talker beats it though.
Keyboardonline.com did an article comparing may vocoders with audio examples, but I can't seem to come up with the link. Must be dead.
[This message has been edited by FAEbGBD (edited 02-28-2002).]