You can craft a URL that will take advantage of Google's web service to do test-to-speech of arbitrary English text like this http://translate.google.com/translate_tts?tl=en&q;=some+text+separated+by+plus+signs
This can easily be extended to work in a form. (Note, I found by trial-and-error that the text cannot have more than about 100 characters, so I limited how much you can type or paste into the text box.)
Try entering some text and to see for yourself!
There was some problem with the Internet Explorer browser. If you get a "not found" error page, try refreshing the error page. That worked for me.
It worked fine in the Google Chrome browser. (tags: webservices)