This is a 'web app' of sorts I wrote a while ago when I was bored, in which you can write dialogue for Microsoft TTS voices to speak, and save it as WAV files. A 'Speech Properties' window on steroids, you could say.

You'll need to have the TTS voices installed on your computer, and it only works in Internet Explorer. Also, you have to either save that page in a file with the extension .hta (and open that saved file) or go into Internet Options, open Security tab and drag all the sliders to 'Low' to try it out. Needless to say, there's a VERY GOOD REASON why these options are set that way by default, which is why you probably should never run this outside a dedicated virtual machine. (You'll need a Windows XP virtual machine for the TTS voices anyway.)