Here is a mostly complete list of offline text-to-speech engines I have at my disposal. I have cleaned up the text somewhat from the last time, so they should be easier to understand. Let me know what your favorite is in the comments.
Espeak is a very robotic, but relatively lightweight engine:
Festival is a quirky, but also lightweight engine. It was developed at the University of Edinburg, so it has a distinctly Scottish accent, which is cool:
Pico was developed by a company called SVOX, and was chosen by Google to be the voice of Android 1.6 “Donut”:
There is also Festival Light developed at CMU, it has a variety of voices available to it: