I remember seeing a video from Craig Knudsen for Yamaha that had total pitch correction software for their keyboards. He sung the national anthem totally off key and flat- the processor made him sound like a professional arena singer..amazing. I don't think that made it into their keyboards after the beta test though.
In fact, here it is! Come to think of it, I might have seen it here.

Pitch Correction-Krazy Kooky Korrection Karaoke