NaturalReader Text to Speech is a powerful tool that will allow you to convert any text on your screen to speech with numerous different language and voice options. It offers a tutorial when you first start the app, which is good because there are quite a few options to sort out.
After loading the app, you can do a number of things, including connect the app to your Dropbox account or Skydrive, load files from the Web, copy and paste, or type text directly into the interface and have it read back to you. At any time you can open a file and edit it or have it read to you. It's easy to switch the reading position onscreen by tapping a section with your finger, and there are five languages (and two options for English), along with more than two dozen total voices you can choose from across those languages. The interface is very clean, the performance is fast and responsive, and you can make so many changes that if you don't like a particular read-through, there are plenty of ways to change it.
NaturalReader Text to Speech is a great app that works well for anyone with large volumes of text they need to have read back to them. It's fast, easy to use, and free, and it has some decent voices to choose from.