Just to reiterate: You definitely can do text to speech using apps on the LCD side. Currently the eInk side does not do text to speech.

If you have DRM-protected EPUBS/PDFs which you want read out via TTS, you may not be able to find an app for the LCD side that can read these protected items. From what I've seen in the past year, most free apps only deal with unprotected ebooks. Kindle, Borders and B&N have an LCD app for (their) protected content, but I don't think they do TTS nor do they open DRM ebooks from other sources.