What software can allow you to change your voice?

And I mean, before any program like Ventrilo gets a hold of it. I know there are some voice changers that are compatible with vent, but I want one that takes the voice input and changes it, then pes it on so that I never have to worry whether or not it's compatible with a program I use. Also I'd like to be fairly customizable. Would prefer freeware but shareware/paid programs are OK too, provided they're worth the price.