An open access e-books site run by O'Reilly Media that contains both in-print and out-of-print texts on various topics such as Linux, MySQL, Samba, Java and CGI programming

This site lists freely available online computer science and engineering books (and lecture notes). You can also receive updates and information about newly added books via an RSS feed included on the site. Also check out their links to other free e-book sites on the Web

Another free site listing links to e-books in many different subjects, including C and C++, Perl, Java and security