Google has it's own app TTS for Android
I have never tested it though. It can be used to read text on screen, such as reading the books in Google Play Books; can you sideload books and then open them with Google Books? I've never tested this.
Maybe I should. I can understand English spoken at blistering speed if I have to; much faster than I could ever read. Maybe using TTS, I could "read" more books...
Take a look at this also
TTS apps, specifically for books, or ebook apps that can do TTS as well.
The big mama's are in there I see: Mantano, Moon+, Coolreader...