From: CaliforniaRural on
I know of two free SAPI5 voices that are not Microsoft voices.
However, I don't think either one is better than the Microsoft voices.
The first one is "CMU Kal Diphone Voice". This voice can be found
here.
http://www.bytecool.com/voices.htm



The second voice is eSpeak. It is located here.
http://espeak.sourceforge.net/

Following up these voices may give you information about building one
yourself. I thought I came across information about this when I was
looking for the CMU Kal Diphone Voice. However, I am not knowledgeable
in this area. So, I am not sure what I found.