As noted in our write-up of e-books at a Chicago parochial school, readers can already enjoy a wealth of good resources online.
You can download gems ranging from first-class lesson plans to fairy tale collections. Also enjoy books from Project Gutenberg, the Internet Public Library, the On-Line Books Page, the English Server, the Electronic Text Center at the University of Virginia, and the University of California Press.
With links to so many other resources, the Internet Public Library might be the best single place to start.
The just-given links will lead you to thousands of titles. Although TeleRead would vastly improve matters, it isn't as if the Net right now is a total wasteland. What's more, BookShare.org will soon offer a legal way for people with print-related disabilities to be able to share many books.
Here are a few more existing resources:
--Yahoo's listing of electronic book publishers. They range from Peanut Press (offering software for Palm computers) to Time Warner Bookmark. Among other things AOL Time Warner owns iPublish, a wonderful concept in theory even though the contracts are stacked against the new writers who use the service.
To see how other people are benefiting from e-books in The Real World, you can read Wired Libraries for Kids and Parents: What's Out There Now--and What Should Be. Also check out E-Book Observations and Tips from Readers and Vendors.