I just ordered a Boss VF-1 and had it plugged in for the first time today. This is a multi-fx unit. But, it has this sweet function on there where you can absolutely make your voice sound like anything: a chipmunk, a kid, a woman, a man, a giant, a very low giant with a chipmunk's tonality, a lady with a big beefy sound, just anything. It does them all quite well in my opinion. I've never had another unit that did anything like it, so I can't compare it to other equipment, but I was mightily impressed. I don't think you could sound like a pure, sweet-voiced woman if you have a raspy voice though.
The vf-1 follows your voice exactly, so speaking into a mic running the VF-1 will work for speaking or singing. There is a slight bit of residual voice bleed from time to time, so it might take a couple takes sometimes to get it just right.