Check out Autotune and just about any dely, chorus, pitch-shift, compression, expansion and EQ plugin.
To my knowledge there aren't a whole lot of all-in-one plugs that do just vocal processing that are all that great - if only because its generally better and more CPU efficient to build the same set of effects as needed with individual plugs.
But that's my bias and may well be the reason that I don't know of many vocal specific plugs. Hopefully someone will happen along that knows more about them, and about AU plugs, than I do.
an older plugin I quite liked in my VST days was the "Yamaha vocal rack" it had a compressor section, EQ, DeEssing, Delay and harmonic saturation. Very handy, worked well on other stuff too, not just vocals
Have a look at the Voxengo Voxformer. I haven't tried it yet, but I use other Voxengo products, and have always been impressed with them. This isn't a voo-doo plugin, just Voxengo's approach to the usual vocal channel strip plug. Should be worth trying the demo (I'm gonna).
For pitch control, I've had good results with Anteres Autotune - IF you use it correctly. It's fine for minor periodic intonation correction, within a few cents, and for tightening up harmonies. It is NOT a garbage in/music out wonderbox.
well you are not going to find one free and your best bet would be to just run out and buy the digitech unit and reamp vocals through it or just plain set up some good VST and AU plugs for the desired effects you want, garage band has most of those things built in also in case you had not fooled with it enough.
i'm not necessarily looking for sometime free. i'll definitely pay for something good but avox just isn't as feature comprehensive as something i'd want. by the way, anyone know of any octave dividing type AU plugins for mac?