I just discovered Tar Heel Reader, a wonderful resource for finding easy to read books all designed for students with special needs. This site makes it very easy to create your own books tailored to your students, and then to share them with others. Here's an excerpt from their Welcome page:
Welcome to the Tar Heel Reader, a collection of free, easy-to-read, and accessible books on a wide range of topics. The books may be downloaded as slide shows in PowerPoint, Impress, or Flash format. Each book can be speech enabled and accessed using multiple interfaces, including touch screens, the IntelliKeys with custom overlays, and 1 to 3 switches.
You may write your own books using pictures from the huge collection at Flickr or pictures you upload. All books should be complete, edited, and revised to the best of your ability before publishing them to the site. While you are working on them, please save them as drafts.
Note the little home icon in the upper left corner of the page (pictured on the left here). Clicking it will bring you back here.