Project Bartleby - An archive of actual texts of classic childrens' works on the web. Here are some additional resources for digitized text or e-text. Interfaces newsletter - Spring 1998 issue. You can obtain an electronic format of this newsletter from their website. Each book has a software profile with extensive information on the interactive book that has been reviewed by this project.
Most books are at the secondary level.
You cannot request textbooks to be put into e-text format but you have access to books that have already been put into this format.