Best Voice Synthesizer for OS X ???


could somone please tell me if there is a "better" voice
synthesizer out there for OS X ?

I'd be willing to pay dearly.. well, somewhat dearly :)
for a really nice as-close-to-normal-human-speech voice
synthesizer as possible.

none of the voice synths that ship with os x are good enough to
listen to the voice recite a document or chapter.

thanks :)

hoping there is something out there..