MacSpeech  
   Home of iListen, a Speech Dictation/Command software for Mac OS. Includes news releases, online store, and tech support.
   http://www.macspeech.com/

Speechissimo  
   Converts any written text into speech using Elan Sayso text-to-speech technology. Speechissimo can speak multiple common languages. For Mac OS X.
   http://www.speechissimo.com/

Elan Speech  
   Offers Elan Sayso natural sounding text-to-speech for Mac OS X. Available in 12 languages.
   http://www.elanspeech.com/

IBM ViaVoice (US English)  
   Continuous speech recognition for your Mac.
   http://www-306.ibm.com/software/voice/viavoice/mac/

Speech Technologies (Apple)  
   Apple�s Speech Recognition and Speech Synthesis Technologies now give speech-savvy applications the power to carry out your voice commands, and even speak back to you in plain English, and now, Spanish.
   http://www.apple.com/macosx/features/speech/