Text to Speech

Safari
Use the built-in Speak Selection in Safari to read webpages
Settings > General > Accessibility > Speak Selection > Highlight Words
The Safari Reader mode cleans up websites. Try it here!

Pocket
This app lets you save articles to read later, offline.
It also cleans up articles to make them easier to read. Works with speak selection.
Save articles to Pocket from the web browser or via email

Readability
Similar to Pocket
Gives articles a very clean and easy to read format
Has a variety of themes and fonts. Works with Speak Selection.

SpeakIt!    
Copies emails, documents, web pages and pdf files into SpeakIt and the text is then spoken back to you. 
Can also create audio files of the TTS that can be saved and emailed.

ClaroSpeak    
Can import and read documents, pptx and epub files. 
Uses visual higlighting of text as it reads. Customizable font size and color contrasts are available. Can also be used to create audio files from text.

Write and Say   
Text editor with advanced speech and translation capabilities that converts your text into natural-sounding speech. Integrates with Google translate that requires internet access. Option to create audio files for use on other devices is also included.

VBookz PDF Reader    
Text to speech with highlighting as it reads for PDF files using high quality voices.    
Can import PDFs from Safari, email or Dropbox.