Looking around for free text to speech software (or web-based solutions), I found these:
http://text-to-speech.imtranslator.net/ - Best one I came across. It's completely free and offers several different languages.
YAKiToMe - Not bad, I found the pronounciation of slightly lesser quality than the previous site. But YAKiToMe allows you to upload PDFs (if you have an eBook in PDF format, for instance) and it will read the whole thing to you. Registration is free.
Mac OSX comes with a command-line tool "say". There's not really an equivalent that comes with Windows, but I found this Windows-executable which does the same thing. It uses the built-in Windows voice. (in case that previous link ever stops working: Here's a perma-link to the executable and here's the source code)
Cepstral - This one is not free (even though there's a demo on their website) but the voices and pronounciation are very good.