Well, I don't have a vocoder yet, but I've taken out a loan which I'm sharing with a freind of mine who's in dire financial situations, so I'm spending the remaining £2,000 on some gear...

A Yamaha A4000
Electrix Warp Factory Vocoder
Some FX unit...forgot which one I liked in the shop...was it the 'Studio 500'?
Another FX unit with a realtime parameter knob to change pitch....
And the new Alesis AirFX.

Then I'll be set up to make any music I like, and with the right gear to perform live on stage...
I'll be playing back most of my tracks from my EMU XL-1 thru MIDI from my computer, and as for the LIVE involvment I'll be playing custom sounds from my Korg 01/W through the AirFX, and splitting off the ouput of that into the vocoder which I will be gabbering into with a cordless headset mic.
I'm not after creating robot sounds...I'll avoid that as much as poss but try and use my voice, with pitch shifting and vocoding....it'll be strange.

With the gear I'm about to buy, it should eb so flexible that I'm really exactly sure how I'll connect it all up!

I suppose you're looking for a software vocoder though - that's not my scene because as a musician aiming for LIVE performance I need to have all the controls at my fingertips, that means having real knobs that I can tweak at an instant rather than having to go back to the computer and getting the mouse cursor on the virtual controls...