From classics required for class reading to monthly magazines, many publications are available for free online. The following sites allow you to download books and other material at no cost, letting you read them on a computer or select mobile devices almost instantly.
Google Books - Extensive catalog of free e-books. Fiction, nonfiction, magazines and more.
Electronic Literature Foundation - ELF features advanced electronic texts of Western classical works "to be used by students, scholars, and admirers of literature around the world." Their library currently holds 129 works by 20 authors, from Dante to Voltaire, all accessible for free.
English Online Resources - The Virtual Library of Virginia (VIVA) makes available thousands of titles, many in the public domain. Although some texts are only available to affiliates of VIVA, if you're looking for literary classics you'll find some treasures here.