3 Replies
Steve Flowers

Ivona voices are pretty good. Any of the better voices out there are going to cost a bit of cash. For elearning purposes, ivona studio starts at $650. 

http://www.ivona.com/

If you have access to a Mac, the VoiceOver voices can be decent as well (not the defaults, the downloads) and you can script through terminal to have text spoken to an audio file.