Local libraries offer a great opportunity to read for free or you can use World Public Library
Project Gutenberg I appreciate this free resource because it offers over 60,000 titles and many of their books out of print interest me.
International Children's Library This is a good resource when searching for titles for littles.
Open Library- is another good resource for free books
Library Thing- I've used this to obtain free books
Goodreads Free Reads- Many I know use this to read online
Little Free Library –. If you type this into my blog's search field. You will see that I donate and receive books from little free libraries. Individuals and stewards of Little Free Library are eligible to receive free books.
Better World Books – books are donated to organizations for the cost of shipping. They have a bargain and used bins too.
Dolly Parton’s Imagination Library – families of children under 6 who live in select areas around the world can receive one free book a month
First Book Marketplace – Book Bank – First Book members can order free books but must pay shipping and handling costs if the books are to be delivered
International Book Project – this project was created for children in parts of the United States and some international locations to receive free books
Library of Congress Surplus Books Program are provided to institutions and organizations that meet their criteria
Literacy Empowerment Foundation – 100 book sets are sent through their Reading Resource Project at the cost of shipping, handling, and administrative fees to promote literacy-based efforts
Many of these places also are in need of donations to help support their efforts in providing free books.