They definitely make rackmount ones that will do it live without a computer. This band from around here that everybody hates uses one and it sounds like shit, and everybody makes fun of them for it, but he uses it constantly on every song for some reason. go to their myspace page here:
and listen to their shitty terrible horrible god awful cover of that Katy Perry song "Hot n cold"... that's him using his stupid rack mount auto tuner that he uses live.
Yeah rob, just plug a mic into a ps-3, ps-5, or whammy pedal, than plug that into your p.a. A wireless unit would be effective, and a wireless from the pedal to a clip on amp. NOW I WANT TO DO THIS.
Now this only works in theory, same as using an octive pedal that tracks terribly, you could even throw some dist. or flanging/phasing on it to really sound weird.
You could also use a pog or a hog, but I think you'll end up getting sounds like Dan Decon ala the high pitched parts in "Crystal Cat." Pitchshifters sound like the best bet, that or modifying Halloween voice changing toys.