Junior Library Guild currently has free e-book access available for all grade levels. There's no limit to the number of users who can access the books.
To get them, click on over to https://jlg.ipublishcentral.com/
Then use the following codes depending on grade level:
Elementary
Username: JLGELM
Password: JLGFREE
Middle
Username: JLGMID
Password: JLGFREE
High School
Username: JLGHI
Password: JLGFREE