Books Online:

Google Books Searchable collection of books which are out of copyright. 
iBooks The iBooks app makes downloading ebooks, or iBooks, easy.
World Public Library For an annual membership fee (presently $8.95) users may access collections of classic and uncopyrighted books, audiobooks, and government publications. A School eBook Library collection promises student-appropriate titles.  The children's collection contains about 1000 classic books.

For elementary students:
IPL Story pages
Stories for young people from the Internet Public Library.

Teacher Tap Electronic books and online reading & writing

For Jr/High and Adults:
Project Gutenberg
"Project Gutenberg is the Internet's oldest producer of free electronic books (eBooks or etexts)."
        -P.G. web site
Daily Lit
DailyLit sends books in installments via e-mail or RSS feed.  Many books are free, and you can read ahead by requesting additional installments at your convenience.
Fang - a Maximum Ride novel  This installment of this popular series is available online. An audio version of the first half of the book is also available as a free download. (The full audiobook is at iTunes)
Yoza  Find short stories and serial stories that can be downloaded to your PC or phone at this South African site.  If you like to write, you can also submit your stories or reviews to be shared under a Creative Commons license.  

updated 18 Nov. 2012