The Accessible Book Collection is a website for acquiring digital text. The books available in several different formats - Clicker 5, Classroom Suite, & Boardmaker Plus format. The majority of the books are in XHTML, which can be used with text readers, & text readers in web browsers. Many of the books in this collection are geared toward older students - a quick browse shows a listing for Twighlight & Harry Potter.
The Accessible Book Collection is not free (sorry, can't have it all!). It has a small subscription fee of $50 per year, there are discounts for multiple subscriptions (such as for a school). They are adding books everyday, so check out what they have.
Accessible Books Collection