Dragon NaturallySpeaking is the leader in speech recognition software and is available in several formats. While the Dragon desktop software for both PC and Mac is pricey, the Dragon Notes app for Windows 8 devices is very affordable, and the Dragon Dictation app for iOS devices is free.
NVDA is a free screen reader that you can download on any Windows device.
Speak it! is an inexpensive iPad/iPhone/iPod Touch app that can read emails, documents, web pages, etc. that are copied and pasted into the application. The words are highlighted as they are read to you. This app also allows users to record and share audio files.
Web Reader HD is yet another low-cost iPad app that will read web pages aloud directly from your Safari browser (no need to copy and paste the text that you want to hear). In addition, the app can read text, HTML, MS Word, and PDF files downloaded from a cloud storage service like Dropbox. It can also read eBooks if they are available on a web page, such as books available through Project Gutenburg.
iReadWrite is a more expensive (but still affordable) iPad TTS app that does much more than just read text aloud. In addition to the TTS feature (with dual-color highlighting), this app includes many helpful features for writing, such as word prediction, phonetic spell checker, a picture dictionary and more.
IVONA is a free Android TTS app that can read directions, emails, texts, websites and documents in 13 languages.