eSpeak is a Free and compact open source software speech synthesizer for English and other languages. It produces good quality English speech. It uses a different synthesis method from other open source TTS engines, and sounds quite different. It's perhaps not as natural or "smooth", but I find the articulation clearer and easier to listen to for long periods of reading. The program and its data, including several languages, totals about 450K. It can also produce speech output as a WAV file.
Because this is a SAPI 5 voice, it is compatible with JAWS for Windows, Window Eyes, Text Aloud, News Aloud and any program that supports SAPI 5.
Click this link to download a sample of eSpeak reading The Raven by Edgar Allen Poe (compressed as .ogg).
Click this link to download eSpeak from its home page: http://espeak.sourceforge.net.