Yagitalk Festival + Mbrola XPI
(depending on your operating system. You may need to download it first, then open it in Firefox)
The main Yagitalk XPI requires the Festival speech synthesis engine. The above package provides festival, the festival voices, mbrola and a few mbrola voices. Due to the inclusion of mbrola, this package is free for non-commercial usage only, but provides better voice quality.
See YagitalkPackages for an overview of all available packages.