Please try Cereproc's new American HTS voice from their live demo:
From the option list, please choose 'HTS (American male)' and click a ply button.
You can hear very good quality and smooth synthetic speech!
http://www.cereproc.com/

News articles on Cereproc. Although I haven’t got involved with this project, this is a great achievement.

Full list of the news article on Roger’s voice can be seen from here.
http://www.cereproc.com/en/node/314