GttSharp - Google TTS in C#
GttSharp is a tiny .NET library made of one class called Speecher, which enables user to communicate with the Google TTS (Text-to-Speech) service. You can use the received stream of data in any way you want or you can save it to the hard-drive in the *.mp3 format.
You can download the library right here and don't forget to read the help file before using the library.